diff --git a/experiments/io-uring-cancel-spike/.gitignore b/experiments/io-uring-cancel-spike/.gitignore
new file mode 100644
index 000000000..ea8c4bf7f
--- /dev/null
+++ b/experiments/io-uring-cancel-spike/.gitignore
@@ -0,0 +1 @@
+/target
diff --git a/experiments/io-uring-cancel-spike/Cargo.lock b/experiments/io-uring-cancel-spike/Cargo.lock
new file mode 100644
index 000000000..33e1b8191
--- /dev/null
+++ b/experiments/io-uring-cancel-spike/Cargo.lock
@@ -0,0 +1,103 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "bitflags"
+version = "2.13.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b4388bee8683e3d04af747c73422af53102d2bd24d9eadb6cbc100baef4b43f8"
+
+[[package]]
+name = "cfg-if"
+version = "1.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9330f8b2ff13f34540b44e946ef35111825727b38d33286ef986142615121801"
+
+[[package]]
+name = "io-uring"
+version = "0.7.13"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9080b15e63775b9a2ac7dca720f7050a8b955e092ea0f6020a4a80f69998cdc0"
+dependencies = [
+ "bitflags",
+ "cfg-if",
+ "libc",
+]
+
+[[package]]
+name = "io-uring-cancel-spike"
+version = "0.1.0"
+dependencies = [
+ "io-uring",
+ "libc",
+ "tokio",
+]
+
+[[package]]
+name = "libc"
+version = "0.2.186"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "68ab91017fe16c622486840e4c83c9a37afeff978bd239b5293d61ece587de66"
+
+[[package]]
+name = "pin-project-lite"
+version = "0.2.17"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a89322df9ebe1c1578d689c92318e070967d1042b512afbe49518723f4e6d5cd"
+
+[[package]]
+name = "proc-macro2"
+version = "1.0.106"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8fd00f0bb2e90d81d1044c2b32617f68fcb9fa3bb7640c23e9c748e53fb30934"
+dependencies = [
+ "unicode-ident",
+]
+
+[[package]]
+name = "quote"
+version = "1.0.46"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dfbc457d0c7a0759a614551b11a6409e5951f6c7537be1f1b7682b9ae9230368"
+dependencies = [
+ "proc-macro2",
+]
+
+[[package]]
+name = "syn"
+version = "2.0.118"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1b9ae57f904213ebb649ce6895b8a66c66f0203b9319718f69a5612a065b1422"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
+
+[[package]]
+name = "tokio"
+version = "1.52.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8fc7f01b389ac15039e4dc9531aa973a135d7a4135281b12d7c1bc79fd57fffe"
+dependencies = [
+ "pin-project-lite",
+ "tokio-macros",
+]
+
+[[package]]
+name = "tokio-macros"
+version = "2.7.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "385a6cb71ab9ab790c5fe8d67f1645e6c450a7ce006a33de03daa956cf70a496"
+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "unicode-ident"
+version = "1.0.24"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e6e4313cd5fcd3dad5cafa179702e2b244f760991f45397d14d4ebf38247da75"
diff --git a/experiments/io-uring-cancel-spike/Cargo.toml b/experiments/io-uring-cancel-spike/Cargo.toml
new file mode 100644
index 000000000..6e65db1a5
--- /dev/null
+++ b/experiments/io-uring-cancel-spike/Cargo.toml
@@ -0,0 +1,20 @@
+[package]
+name = "io-uring-cancel-spike"
+version = "0.1.0"
+edition = "2024"
+publish = false
+description = "Spike 0 for backlog#894 (P2 io_uring read backend): cancel-safety / buffer-ownership prototype. NOT production code."
+
+# Deliberately a standalone workspace: P2 is deferred (P1.5 NO-GO), so the
+# io-uring crate must not enter the main rustfs Cargo.lock or build graph.
+[workspace]
+
+[dependencies]
+tokio = { version = "1", default-features = false, features = ["sync"] }
+
+[target.'cfg(target_os = "linux")'.dependencies]
+io-uring = "0.7"
+libc = "0.2"
+
+[dev-dependencies]
+tokio = { version = "1", features = ["rt-multi-thread", "macros", "sync", "time"] }
diff --git a/experiments/io-uring-cancel-spike/SPIKE.md b/experiments/io-uring-cancel-spike/SPIKE.md
new file mode 100644
index 000000000..9ded1323d
--- /dev/null
+++ b/experiments/io-uring-cancel-spike/SPIKE.md
@@ -0,0 +1,99 @@
+# Spike 0: io_uring 取消安全原型(backlog#894 P2 前置)
+
+## 这是什么
+
+rustfs/backlog#897 路线图中 P2(io_uring 读后端)被 P1.5 基准判 NO-GO 而 defer。本 spike 是 #894 明确要求先行的**取消安全原型**——P2 中风险最高、最容易随时间流失的知识,按"只实现原型、不进主干、不启用"的方案 B 存档。重启条件满足前,P2 主体不动工。
+
+**本 crate 是独立 workspace**(Cargo.toml 内含空 `[workspace]` 表),io-uring 依赖不进入 rustfs 主 Cargo.lock、不参与主工程构建与 CI。这与守卫脚本 `scripts/check_no_tokio_io_uring.sh` 的约束一致:禁的是 tokio 的 io-uring runtime feature,应用层显式 io-uring 集成必须走运行时探测的独立后端(即本原型验证的模型)。
+
+## 要证明的问题
+
+EC quorum 达成 / 断连 / 超时会 drop 在途的 `BitrotReaderTask` future(main 上位于 `crates/ecstore/src/set_disk/core/io_primitives.rs:1455` 的 `FuturesUnordered`)。若该 future 已向内核提交了 read SQE,内核在 CQE 之前始终可能向目标 buffer 写入。**future 的 drop 不能回收 buffer,否则是 use-after-free。**
+
+## 验证的所有权模型
+
+```
+caller                    driver thread                     kernel
+------                    -------------                     ------
+read_at() ──Msg::Read──▶  分配 buf,登记 pending 表
+                          (buf + Arc<File> + oneshot tx)
+                          push SQE(user_data=id) ─submit──▶ 开始随时可能写 buf
+await ◀───oneshot────────                                    │
+                                                             │
+future drop(任意时刻)                                        │
+  └─(可选)Msg::Cancel ──▶ push ASYNC_CANCEL ────────────────▶│ 加速 CQE
+  └─绝不触碰 buf                                             │
+                          CQE 到达 ◀─────────────────────────┘
+                          pending.remove(id)  ← 全程唯一的 buf 回收点
+                          send 结果:成功=delivered
+                                    失败(接收方已 drop)=orphan_reclaimed
+```
+
+关键不变量:
+
+1. **buffer 与 fd 归 pending 表所有,不归 future。** SQE 里的裸指针指向表项 `Vec` 的堆块;`Vec` 结构体可随 HashMap 移动(堆块地址不变),但在 CQE 前绝不 resize/drop。
+2. **fd 也必须由表项持有**(`Arc<File>`)。真正的危险窗口是 **SQE 构造(`as_raw_fd`)→ `io_uring_enter` 内核消费**:此窗口内 SQE 携带裸 fd 号在 backlog 中滞留、内核尚未 `fget`;若 fd 被 drop 关闭并被新 `open` 复用,提交时内核解析到错误文件——对 READ op 意味着从**错误文件读出数据**(跨对象数据错读/泄露),而非"内核的写落到别人文件"。表项持有 `Arc<File>` 到 CQE 是该窗口的安全超集。(机理更正见 rustfs/backlog#1063:原文把危险窗口误标为"提交→CQE"、后果误标为"写别人文件"——已提交的 op 因内核已持 struct file 引用而对 fd close/复用免疫;若未来用 SQPOLL,消费点还会与 enter 脱钩。)
+3. **future drop 只放弃结果领取**,默认附带提交 `IORING_OP_ASYNC_CANCEL`(best-effort 加速),也可以不提交(裸 drop)——两种情况下回收都只发生在 CQE。
+4. **shutdown 顺序**:停收新 SQE → 对所有在途 op 提交 cancel → drain 到 `in_flight == 0` → 线程退出 → ring drop(unmap)。ring 决不能在内核仍持有 buffer 引用时 unmap。
+5. **探测必须提交真实 read op**:`io_uring_setup` 成功不代表 op 可用(gVisor/seccomp 可以建 ring 但 op ENOSYS/EINVAL);探测失败按 EACCES/EPERM/ENOSYS/EINVAL/EOPNOTSUPP 分类,命中即优雅降级(测试中表现为 skip),其余 errno 视为真 bug 直接断言失败。
+
+以下不变量是本次审计整改(rustfs/backlog#1051)新增/固化,P2 必须一并沿用:
+
+6. **驱动线程 unwind 安全**(rustfs/backlog#1054):驱动线程绝不允许在栈展开中释放 pending 表或 unmap ring——否则内核仍可能向在途 buffer 写入即 UAF。实现为 `DriverState::Drop` 检测 `thread::panicking()` 时在字段析构前 `process::abort()`(leak over UAF)。所有 caller 可控的 panic 面(如超大 `len`)在 `submit` 入口拒止。`catch_unwind` 不够——析构在展开时、catch 边界之前就已发生。
+7. **背压 permit 在 CQE 点释放**(rustfs/backlog#1060):in-flight 上界 ≤ CQ 容量(取 SQ 深度 `entries` < `2*entries`,使 CQ overflow 结构性不可达),permit 随 pending 表项移除(CQE)释放,**绝不随 future drop 释放**——否则 quorum 大量 drop future 会让 permit 计数与驻留内存脱钩,重开内存 DoS 面。
+8. **复用缓冲内容卫生**(rustfs/backlog#1062,P3 前置):当前 spike 每 op 新分配零页 + `truncate(res)`,**无泄露**。P3 改用驱动自有对齐 slab(registered buffer)后,缓冲跨请求复用即脏内存——任何路径忘记按 `cqe.res` 截断/掩蔽(O_DIRECT 整块读再由上层切片、或错误路径把整块缓冲交还)就把上一租户请求的对象字节泄给当前请求(CWE-226)。不变量:**复用缓冲对调用方可见的字节严格 ⊆ `[0, cqe.res)`**,越界部分零化或由类型系统(返回带长度上限的 view 而非整块 slice)保证不可达。SPIKE.md 与 #1048 原约束只讲 slab 生命周期(防 UAF),不讲内容卫生;需配套"脏缓冲 + 短读"回归测试。
+
+补充契约:
+
+- **errno 三分类**(rustfs/backlog#1059):`is_expected_restriction` **仅用于 probe 期**;运行期 errno 必须分——probe 受限 → 该盘永久降级;运行期参数错误(offset>i64::MAX、O_DIRECT 未对齐等 EINVAL)→ 返回错误、绝不闩锁;瞬态(EINTR/EAGAIN)→ 重试。`submit` 已在入口拒止 offset>i64::MAX 与 len>MAX_RW_COUNT。
+- **shutdown 有界 drain**(rustfs/backlog#1055):drain-to-zero 可能因坏盘上 cancel 不可中断(EALREADY)而不终止;超时(`DRAIN_TIMEOUT`)后泄漏 ring+buffer 退出(leak over UAF),绝不提前 unmap。cancel CQE 三态(succeeded/not_found/already)已纳入统计,EALREADY 上升即坏盘信号。
+- **短读 resubmit**(rustfs/backlog#1058):io_uring 对常规文件可合法短读;驱动 resubmit 剩余到 `buf[nread..]`,回收点移到逻辑读的最后一个 CQE。P2 须明确短读归属(后端循环 vs 调用方 `read_exact`)。
+
+## 测试矩阵
+
+| 测试 | 验证点 |
+|---|---|
+| `read_matches_std` | 完成路径正确性:64 次变长/变偏移读与文件内容逐字节一致 |
+| `dropped_future_buffer_lives_until_cqe` | **核心断言**:阻塞的 pipe 读上裸 drop future(不提交 cancel),300ms 后 op 仍 in-flight、buffer 未回收;向 pipe 写入触发 CQE 后才回收(orphan_reclaimed=1) |
+| `async_cancel_accelerates_reclaim` | 默认 drop 路径:ASYNC_CANCEL 使孤儿 op 在无数据到达的情况下经 ECANCELED CQE 及时回收 |
+| `cancel_stress_accounts_for_every_buffer` | 压力:256 并发读、一半立即 drop;`delivered + orphan_reclaimed == submitted`,幸存读逐字节正确 |
+| `shutdown_drains_in_flight_ops` | 关停:两个阻塞在途 op 被 cancel + drain 到 0 后线程才退出,持有的 future 解析为 ECANCELED |
+
+## 如何运行
+
+需要 Docker(Linux 内核)。macOS 宿主上 `cargo check` 只验证非 Linux 桩编译。
+
+```bash
+./run-docker.sh
+```
+
+- **leg 1(默认 seccomp)**:多数 Docker 版本默认禁 io_uring(即 #4313 事故环境),探测失败 → 全部测试走优雅降级 skip,套件仍绿。若宿主 Docker 放行 io_uring,则此腿等同 leg 2。
+- **leg 2(seccomp=unconfined)**:真实 io_uring,完整跑取消安全套件。
+
+## 运行结果
+
+两腿一次通过,详见"实测记录"。
+
+## 对 P2 主体实现的遗留项(本 spike 不覆盖)
+
+- eventfd + tokio `AsyncFd` 收割替换轮询驱动循环(注意:换收割方式后仍须周期性进 `io_uring_enter(GETEVENTS)` 冲刷 NODROP overflow list,否则 rustfs/backlog#1056 的挂起会复现)。
+- 进程级单例 ring 的生命周期管理(本 spike 每测试一个 ring);Drop 路径不得无界阻塞 tokio worker。
+- O_DIRECT 对齐 buffer(P1 的 statx 探测复用)、三条读形态接入 `LocalIoBackend`。
+- per-disk 探测缓存与运行期 errno 降级闩锁(参照 main 上 `DirectIoReadState`,`crates/ecstore/src/disk/local.rs`;运行期 errno 分类须按不变量补充里的三分类,勿复用 probe 期分类)。
+- registered buffers(P3,内容卫生见不变量 8 / rustfs/backlog#1062)/写路径(P4)完全不涉及。
+
+**已在本 spike 内整改**(rustfs/backlog#1051):SQ 深度背压(不变量 7)、驱动线程 unwind 安全(不变量 6)、shutdown 有界 drain、CQ overflow/NODROP/EBUSY 处理、probe UAF、probe 文件安全创建、errno 三分类、len/offset 校验、短读 resubmit。
+
+## 实测记录
+
+2026-07-07,宿主 macOS + OrbStack Docker(Linux arm64,内核 7.0.11-orbstack),镜像 `rust:1-bookworm`,`cargo test --release`:
+
+- **leg 1(默认 seccomp)**:`io_uring_setup` 失败 `EPERM (Operation not permitted)`——与 #4313 事故环境同类。`ProbeFailure::is_expected_restriction()` 命中,5 个测试全部优雅降级 skip,套件绿。证明探测 + errno 分类降级契约按设计工作。
+- **leg 2(seccomp=unconfined)**:5 个测试全部通过(0.45s):
+  - `read_matches_std` ok — 64 次读逐字节正确;
+  - `dropped_future_buffer_lives_until_cqe` ok — 裸 drop 后 op 保持 in-flight 300ms、buffer 未回收,写 pipe 触发 CQE 后 `orphan_reclaimed=1`;
+  - `async_cancel_accelerates_reclaim` ok — ECANCELED CQE 路径回收;
+  - `cancel_stress_accounts_for_every_buffer` ok — 256 op、128 drop,`delivered(128) + orphan_reclaimed(128) == submitted(256)`;
+  - `shutdown_drains_in_flight_ops` ok — drain 到 0 后退出,持有 future 解析为 ECANCELED。
+
+**结论:GO(模型可行)。** buffer/fd 归驱动 pending 表、CQE 唯一回收点、ASYNC_CANCEL 加速、shutdown drain 的组合在真实内核上成立,且降级契约在受限环境下按设计生效。P2 主体重启时可直接沿用此所有权模型。
diff --git a/experiments/io-uring-cancel-spike/run-docker.sh b/experiments/io-uring-cancel-spike/run-docker.sh
new file mode 100755
index 000000000..41030ba6f
--- /dev/null
+++ b/experiments/io-uring-cancel-spike/run-docker.sh
@@ -0,0 +1,78 @@
+#!/usr/bin/env bash
+# Copyright 2024 RustFS Team
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Runs the spike test suite in the two environments that matter for P2
+# (backlog#894), and — crucially — ASSERTS which path each leg actually took
+# (rustfs/backlog#1067), so neither leg can silently degenerate into a vacuous
+# pass:
+#
+#   leg 1  io_uring blocked by an EXPLICIT seccomp profile (not the host
+#          Docker default), reproducing the #4313 restricted environment.
+#          Every test MUST degrade to a graceful skip; if none skip, io_uring
+#          was not actually blocked and the leg FAILS.
+#   leg 2  seccomp=unconfined — real io_uring against the host kernel. NO test
+#          may skip; a single skip means io_uring did not really run and the
+#          leg FAILS.
+set -euo pipefail
+cd "$(dirname "$0")"
+
+IMG="${SPIKE_IMAGE:-rust:1-bookworm}"
+CACHE_REG=uring-spike-cargo-registry
+CACHE_TARGET=uring-spike-target
+SECCOMP_PROFILE="$PWD/seccomp-block-uring.json"
+
+# Run the suite once, capturing stdout+stderr (so the tests' "SKIP" lines,
+# printed to stderr, are inspectable).
+run_and_capture() {
+    docker run --rm "$@" \
+        -v "$PWD":/spike:ro \
+        -v "$CACHE_REG":/usr/local/cargo/registry \
+        -v "$CACHE_TARGET":/spike-target \
+        -e CARGO_TARGET_DIR=/spike-target \
+        -e CARGO_TERM_COLOR=always \
+        -w /spike \
+        "$IMG" \
+        cargo test --release -- --nocapture --test-threads=1 2>&1
+}
+
+echo "=================================================================="
+echo "== leg 1: io_uring blocked by explicit seccomp profile (degradation expected)"
+echo "=================================================================="
+leg1_out=$(run_and_capture --security-opt seccomp="$SECCOMP_PROFILE") || {
+    echo "$leg1_out"
+    echo "leg 1 FAILED: the suite errored (a blocked probe must degrade, not fail)"
+    exit 1
+}
+echo "$leg1_out"
+if ! grep -q "SKIP " <<<"$leg1_out"; then
+    echo "leg 1 FAILED: expected graceful-degradation SKIPs but saw none — io_uring was NOT blocked"
+    exit 1
+fi
+
+echo "=================================================================="
+echo "== leg 2: seccomp=unconfined (real io_uring)"
+echo "=================================================================="
+leg2_out=$(run_and_capture --security-opt seccomp=unconfined) || {
+    echo "$leg2_out"
+    echo "leg 2 FAILED: the suite errored"
+    exit 1
+}
+echo "$leg2_out"
+if grep -q "SKIP " <<<"$leg2_out"; then
+    echo "leg 2 FAILED: a test skipped — io_uring did not actually run here (vacuous pass)"
+    exit 1
+fi
+
+echo "both legs passed (leg 1 degraded gracefully, leg 2 ran real io_uring)"
diff --git a/experiments/io-uring-cancel-spike/seccomp-block-uring.json b/experiments/io-uring-cancel-spike/seccomp-block-uring.json
new file mode 100644
index 000000000..b3d4ab784
--- /dev/null
+++ b/experiments/io-uring-cancel-spike/seccomp-block-uring.json
@@ -0,0 +1,11 @@
+{
+  "comment": "Deterministically block io_uring for run-docker.sh leg 1 (rustfs/backlog#1067): io_uring_setup/enter/register return EPERM, so the probe fails with an expected-restriction errno and the suite must degrade to a graceful skip — reproducing the #4313 restricted environment without depending on the host Docker's default seccomp.",
+  "defaultAction": "SCMP_ACT_ALLOW",
+  "syscalls": [
+    {
+      "names": ["io_uring_setup", "io_uring_enter", "io_uring_register"],
+      "action": "SCMP_ACT_ERRNO",
+      "errnoRet": 1
+    }
+  ]
+}
diff --git a/experiments/io-uring-cancel-spike/src/driver.rs b/experiments/io-uring-cancel-spike/src/driver.rs
new file mode 100644
index 000000000..9eca64822
--- /dev/null
+++ b/experiments/io-uring-cancel-spike/src/driver.rs
@@ -0,0 +1,905 @@
+// Copyright 2024 RustFS Team
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+use std::collections::{HashMap, VecDeque};
+use std::fs::File;
+use std::io;
+use std::io::Write as _;
+use std::os::fd::{AsRawFd, FromRawFd};
+use std::os::unix::ffi::OsStrExt;
+use std::pin::Pin;
+use std::sync::atomic::{AtomicU64, Ordering};
+use std::sync::mpsc::{self, RecvTimeoutError, TryRecvError};
+use std::sync::{Arc, Condvar, Mutex};
+use std::task::{Context, Poll};
+use std::thread::JoinHandle;
+use std::time::{Duration, Instant};
+
+use io_uring::{IoUring, opcode, types};
+
+/// Upper bound on how long shutdown waits for in-flight ops to drain before
+/// leaking the ring+buffers and exiting (C4, rustfs/backlog#1055). ASYNC_CANCEL
+/// cannot interrupt an in-execution regular-file read on a D-state/NFS-hung
+/// disk, so drain-to-zero can be non-terminating; this bounds it.
+const DRAIN_TIMEOUT: Duration = Duration::from_secs(5);
+use tokio::sync::oneshot;
+
+/// user_data bit marking the CQE of an `AsyncCancel` SQE itself (as opposed
+/// to the CQE of the read op it targets).
+const CANCEL_BIT: u64 = 1 << 63;
+
+/// `offset` value meaning "use the file's current position" (read(2)
+/// semantics); required for pipes/sockets where pread returns ESPIPE.
+const CURRENT_POSITION: u64 = u64::MAX;
+
+/// Kernel single-read cap: `MAX_RW_COUNT = INT_MAX & PAGE_MASK` (2 GiB − 4 KiB
+/// on 4 KiB pages). io_uring's READ length field is a u32, and any request
+/// above this short-reads. We reject beyond it in `submit` so a `len as u32`
+/// truncation can never silently turn a huge read into a 0-byte "EOF" (C6,
+/// rustfs/backlog#1057); P2 must chunk reads larger than this.
+const MAX_READ_LEN: usize = 0x7fff_f000;
+
+/// Why the probe refused to start the io_uring driver.
+///
+/// Mirrors the P2 degradation contract (backlog#894): a restricted
+/// environment must be recognized and answered with a silent fallback to the
+/// std backend, never surfaced to callers.
+#[derive(Debug)]
+pub enum ProbeFailure {
+    /// `io_uring_setup` itself failed (seccomp/gVisor/old kernel).
+    Setup(io::Error),
+    /// The ring was created but a real `IORING_OP_READ` did not complete
+    /// correctly (gVisor accepts setup but fails ops; also covers silent
+    /// data corruption, which we treat as "unusable").
+    ReadOp(io::Error),
+}
+
+impl ProbeFailure {
+    /// True when the **probe-time** errno belongs to the "expected
+    /// restriction" class that P2 maps to permanent per-disk fallback:
+    /// EACCES/EPERM/ENOSYS/EINVAL/EOPNOTSUPP. Anything else is a genuine bug
+    /// worth surfacing.
+    ///
+    /// IMPORTANT (C7, rustfs/backlog#1059): this classification is valid ONLY
+    /// for a one-shot startup probe, where these errnos unambiguously mean
+    /// "io_uring is unusable here" (gVisor/seccomp/old kernel). Runtime
+    /// per-op errnos have different semantics and MUST NOT reuse this class.
+    /// In particular EINVAL is triple-meaning at runtime — offset > i64::MAX
+    /// (signed loff_t), O_DIRECT buffer/offset/len misalignment (P2 will use
+    /// O_DIRECT), and setup `entries` over the cap — none of which imply the
+    /// disk should be permanently degraded off io_uring. P2's degradation
+    /// contract must split errnos into three classes:
+    ///
+    ///   * probe-time restriction  -> degrade this disk to the std backend;
+    ///   * runtime parameter error -> return the error to the caller (and,
+    ///     for a suspected bug, re-verify once via std pread) — never latch;
+    ///   * transient (EINTR/EAGAIN) -> retry, never surface.
+    ///
+    /// See `submit` for the offset guard that keeps a caller arithmetic bug
+    /// from ever reaching the kernel as a runtime EINVAL.
+    pub fn is_expected_restriction(&self) -> bool {
+        let err = match self {
+            ProbeFailure::Setup(e) | ProbeFailure::ReadOp(e) => e,
+        };
+        matches!(
+            err.raw_os_error(),
+            Some(libc::EACCES) | Some(libc::EPERM) | Some(libc::ENOSYS) | Some(libc::EINVAL) | Some(libc::EOPNOTSUPP)
+        )
+    }
+}
+
+/// Submission-side backpressure (C10, rustfs/backlog#1060).
+///
+/// Bounds in-flight ops so the count can never exceed CQ capacity, and — the
+/// load-bearing part — releases a permit at the CQE (pending-table removal),
+/// NOT at future drop. Tying a permit to the future (the natural RAII shape)
+/// would let a quorum dropping many futures return permits while their orphan
+/// buffers still sit in the pending table awaiting slow-disk CQEs, decoupling
+/// the permit count from resident memory and reopening the memory-DoS surface.
+/// P2 uses a tokio `Semaphore` with `acquire_owned`; the RELEASE POINT is what
+/// matters and must stay at the CQE.
+struct Backpressure {
+    state: Mutex<BpState>,
+    cv: Condvar,
+}
+
+struct BpState {
+    permits: usize,
+    shutdown: bool,
+}
+
+impl Backpressure {
+    fn new(permits: usize) -> Self {
+        Self {
+            state: Mutex::new(BpState {
+                permits,
+                shutdown: false,
+            }),
+            cv: Condvar::new(),
+        }
+    }
+
+    /// Block until a permit is free. Returns false if the driver has shut down
+    /// (so submit stops blocking forever once the driver is gone).
+    fn acquire(&self) -> bool {
+        let mut g = self.state.lock().expect("backpressure mutex poisoned");
+        loop {
+            if g.shutdown {
+                return false;
+            }
+            if g.permits > 0 {
+                g.permits -= 1;
+                return true;
+            }
+            g = self.cv.wait(g).expect("backpressure mutex poisoned");
+        }
+    }
+
+    fn release(&self) {
+        let mut g = self.state.lock().expect("backpressure mutex poisoned");
+        g.permits += 1;
+        self.cv.notify_one();
+    }
+
+    fn shutdown(&self) {
+        let mut g = self.state.lock().expect("backpressure mutex poisoned");
+        g.shutdown = true;
+        self.cv.notify_all();
+    }
+}
+
+#[derive(Default)]
+struct DriverStats {
+    submitted: AtomicU64,
+    delivered: AtomicU64,
+    orphan_reclaimed: AtomicU64,
+    in_flight: AtomicU64,
+    cancel_succeeded: AtomicU64,
+    cancel_not_found: AtomicU64,
+    cancel_already: AtomicU64,
+    cq_overflow: AtomicU64,
+}
+
+/// Point-in-time copy of the driver counters.
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub struct StatsSnapshot {
+    /// Read ops handed to the kernel.
+    pub submitted: u64,
+    /// CQEs whose result was received by a live caller.
+    pub delivered: u64,
+    /// CQEs whose caller had dropped the future: the buffer stayed in the
+    /// pending table the whole time and was reclaimed here, at the CQE.
+    pub orphan_reclaimed: u64,
+    /// Ops submitted but not yet completed. The kernel may still write into
+    /// their buffers.
+    pub in_flight: u64,
+    /// ASYNC_CANCEL CQEs that reported the target op was canceled (res == 0).
+    pub cancel_succeeded: u64,
+    /// ASYNC_CANCEL CQEs that reported the target was not found (-ENOENT):
+    /// the op had already completed.
+    pub cancel_not_found: u64,
+    /// ASYNC_CANCEL CQEs that reported the target was already executing and
+    /// could not be interrupted (-EALREADY). A rising count is the hung-disk
+    /// signal that makes drain-to-zero non-terminating (C4,
+    /// rustfs/backlog#1055).
+    pub cancel_already: u64,
+    /// Kernel CQ-ring overflow counter. MUST stay 0: a non-zero value means
+    /// CQEs were lost, so their pending entries are never reclaimed and drain
+    /// never completes. Treated as fatal (C5, rustfs/backlog#1056).
+    pub cq_overflow: u64,
+}
+
+enum Msg {
+    Read {
+        id: u64,
+        file: Arc<File>,
+        offset: u64,
+        len: usize,
+        done: oneshot::Sender<io::Result<Vec<u8>>>,
+    },
+    Cancel {
+        id: u64,
+    },
+    Shutdown,
+}
+
+/// One in-flight LOGICAL read. This struct — not the caller — owns everything
+/// the kernel touches:
+///
+/// - `buf`: the destination buffer. Its heap allocation must stay put until
+///   the final CQE; the `Vec` itself may move (HashMap rehash) since that
+///   never relocates the heap block. It is never resized or dropped before
+///   the CQE handler removes this entry.
+/// - `file`: keeps the fd open even if every caller-side clone is dropped, and
+///   supplies the fd for short-read resubmission. Without it, dropping the
+///   future could close the fd while an SQE built from that fd still sits in
+///   the backlog (SQE construction → io_uring_enter window), and a recycled
+///   fd number would make the kernel read the WRONG file (spike finding, with
+///   the corrected mechanism per rustfs/backlog#1063).
+/// - `offset`/`nread`: track a short-read resubmit loop (C9,
+///   rustfs/backlog#1058). io_uring may legally short-read a regular file;
+///   the driver resubmits the remainder into `buf[nread..]` until the request
+///   is fully satisfied or a real EOF (res == 0) is seen, so reclamation
+///   happens only at the FINAL CQE of the logical read.
+struct Pending {
+    buf: Vec<u8>,
+    file: Arc<File>,
+    done: Option<oneshot::Sender<io::Result<Vec<u8>>>>,
+    offset: u64,
+    nread: usize,
+}
+
+/// Handle to a submitted read. Await it for the result.
+///
+/// Dropping it before completion abandons the result only; by default it
+/// also submits `IORING_OP_ASYNC_CANCEL` (best effort) so the CQE — and with
+/// it the buffer reclamation — arrives sooner. `without_cancel_on_drop`
+/// disables that to model the bare "quorum drops the future" case.
+pub struct ReadHandle {
+    id: u64,
+    rx: oneshot::Receiver<io::Result<Vec<u8>>>,
+    tx: mpsc::Sender<Msg>,
+    finished: bool,
+    cancel_on_drop: bool,
+}
+
+impl ReadHandle {
+    pub fn without_cancel_on_drop(mut self) -> Self {
+        self.cancel_on_drop = false;
+        self
+    }
+}
+
+impl Future for ReadHandle {
+    type Output = io::Result<Vec<u8>>;
+
+    fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        match Pin::new(&mut self.rx).poll(cx) {
+            Poll::Ready(res) => {
+                self.finished = true;
+                Poll::Ready(match res {
+                    Ok(inner) => inner,
+                    Err(_) => Err(io::Error::other("uring driver shut down before completion")),
+                })
+            }
+            Poll::Pending => Poll::Pending,
+        }
+    }
+}
+
+impl Drop for ReadHandle {
+    fn drop(&mut self) {
+        // The buffer is deliberately NOT touched here: the driver owns it
+        // until the CQE. All we may do is ask the kernel to hurry up.
+        if !self.finished && self.cancel_on_drop {
+            let _ = self.tx.send(Msg::Cancel { id: self.id });
+        }
+    }
+}
+
+/// Process-level io_uring driver: one ring, one driver thread.
+pub struct UringDriver {
+    tx: mpsc::Sender<Msg>,
+    handle: Option<JoinHandle<()>>,
+    stats: Arc<DriverStats>,
+    next_id: AtomicU64,
+    bp: Arc<Backpressure>,
+}
+
+impl UringDriver {
+    /// Create the ring AND verify a real `IORING_OP_READ` round-trip on a
+    /// temp file before accepting work. `io_uring_setup` succeeding is not
+    /// enough: gVisor/seccomp environments can create a ring whose ops then
+    /// fail with ENOSYS/EINVAL (backlog#894 probe design).
+    pub fn probe_and_start(entries: u32) -> Result<Self, ProbeFailure> {
+        let mut ring = IoUring::new(entries).map_err(ProbeFailure::Setup)?;
+        // Require the NODROP feature (kernel >= 5.5). Without it, CQ overflow
+        // silently drops CQEs, stranding pending entries forever and hanging
+        // shutdown (C5, rustfs/backlog#1056). ENOSYS is in the expected-
+        // restriction class, so this degrades to the std backend cleanly.
+        if !ring.params().is_feature_nodrop() {
+            return Err(ProbeFailure::Setup(io::Error::from_raw_os_error(libc::ENOSYS)));
+        }
+        probe_real_read(&mut ring).map_err(ProbeFailure::ReadOp)?;
+
+        let (tx, rx) = mpsc::channel();
+        let stats = Arc::new(DriverStats::default());
+        let thread_stats = Arc::clone(&stats);
+        // Cap in-flight at the SQ depth (entries), which is < CQ capacity
+        // (2*entries), so CQ overflow is structurally unreachable (C5/C10).
+        let bp = Arc::new(Backpressure::new(entries as usize));
+        let thread_bp = Arc::clone(&bp);
+        let handle = std::thread::Builder::new()
+            .name("uring-spike-driver".into())
+            .spawn(move || drive(ring, rx, thread_stats, thread_bp))
+            .expect("spawn driver thread");
+
+        Ok(Self {
+            tx,
+            handle: Some(handle),
+            stats,
+            next_id: AtomicU64::new(1),
+            bp,
+        })
+    }
+
+    /// Positioned read (pread semantics) — regular files.
+    pub fn read_at(&self, file: Arc<File>, offset: u64, len: usize) -> ReadHandle {
+        assert_ne!(offset, CURRENT_POSITION, "offset u64::MAX is reserved");
+        self.submit(file, offset, len)
+    }
+
+    /// Read at the file's current position (read(2) semantics) — pipes.
+    pub fn read_current(&self, file: Arc<File>, len: usize) -> ReadHandle {
+        self.submit(file, CURRENT_POSITION, len)
+    }
+
+    fn submit(&self, file: Arc<File>, offset: u64, len: usize) -> ReadHandle {
+        let id = self.next_id.fetch_add(1, Ordering::Relaxed);
+        assert_eq!(id & CANCEL_BIT, 0, "op id overflowed into the cancel bit");
+        let (done, rx) = oneshot::channel();
+
+        // Reject an offset the kernel would answer with a runtime EINVAL that
+        // must NOT be mistaken for an environment restriction (C7,
+        // rustfs/backlog#1059). The kernel reads `off` as a signed loff_t, so
+        // offset > i64::MAX becomes a negative ki_pos → EINVAL. A caller
+        // offset-arithmetic bug has to surface as an error here, never as a
+        // permanent per-disk fallback. CURRENT_POSITION is the reserved
+        // read(2) sentinel and bypasses this check.
+        if offset != CURRENT_POSITION && offset > i64::MAX as u64 {
+            let _ = done.send(Err(io::Error::new(
+                io::ErrorKind::InvalidInput,
+                "offset exceeds i64::MAX (kernel loff_t is signed)",
+            )));
+            return ReadHandle {
+                id,
+                rx,
+                tx: self.tx.clone(),
+                finished: false,
+                cancel_on_drop: false,
+            };
+        }
+
+        // Reject a length the kernel would short-read past MAX_RW_COUNT and
+        // that the SQE's u32 `len` field would silently truncate: len == 2^32
+        // becomes a 0-byte read the caller decodes as a false EOF (C6,
+        // rustfs/backlog#1057). Failing fast here also removes the caller-
+        // controlled `vec![0u8; len]` capacity-overflow panic that made the
+        // unwind-UAF (rustfs/backlog#1054) reachable. P2 must chunk instead.
+        if len > MAX_READ_LEN {
+            let _ = done.send(Err(io::Error::new(
+                io::ErrorKind::InvalidInput,
+                "read length exceeds MAX_RW_COUNT (2 GiB - 4 KiB); caller must chunk",
+            )));
+            return ReadHandle {
+                id,
+                rx,
+                tx: self.tx.clone(),
+                finished: false,
+                cancel_on_drop: false,
+            };
+        }
+
+        // Acquire a backpressure permit BEFORE handing the op to the driver;
+        // the driver releases it at the CQE (C10, rustfs/backlog#1060). This
+        // blocks the caller once `entries` ops are in flight, bounding both
+        // in-flight count (< CQ capacity) and resident buffer memory.
+        if !self.bp.acquire() {
+            let _ = done.send(Err(io::Error::other("uring driver shut down")));
+            return ReadHandle {
+                id,
+                rx,
+                tx: self.tx.clone(),
+                finished: false,
+                cancel_on_drop: false,
+            };
+        }
+
+        // If the driver shut down between acquire and send, give the permit
+        // back — no CQE will ever release it. `done` is dropped with the
+        // returned Msg, which the caller observes as a driver-gone error.
+        if self
+            .tx
+            .send(Msg::Read {
+                id,
+                file,
+                offset,
+                len,
+                done,
+            })
+            .is_err()
+        {
+            self.bp.release();
+            return ReadHandle {
+                id,
+                rx,
+                tx: self.tx.clone(),
+                finished: false,
+                cancel_on_drop: false,
+            };
+        }
+        ReadHandle {
+            id,
+            rx,
+            tx: self.tx.clone(),
+            finished: false,
+            cancel_on_drop: true,
+        }
+    }
+
+    pub fn stats(&self) -> StatsSnapshot {
+        StatsSnapshot {
+            submitted: self.stats.submitted.load(Ordering::SeqCst),
+            delivered: self.stats.delivered.load(Ordering::SeqCst),
+            orphan_reclaimed: self.stats.orphan_reclaimed.load(Ordering::SeqCst),
+            in_flight: self.stats.in_flight.load(Ordering::SeqCst),
+            cancel_succeeded: self.stats.cancel_succeeded.load(Ordering::SeqCst),
+            cancel_not_found: self.stats.cancel_not_found.load(Ordering::SeqCst),
+            cancel_already: self.stats.cancel_already.load(Ordering::SeqCst),
+            cq_overflow: self.stats.cq_overflow.load(Ordering::SeqCst),
+        }
+    }
+
+    /// Stop accepting work, cancel all in-flight ops, drain the ring to
+    /// `in_flight == 0`, then join the driver thread. Only after that is the
+    /// ring dropped/unmapped — the shutdown ordering P2 requires.
+    pub fn shutdown(mut self) -> StatsSnapshot {
+        let _ = self.tx.send(Msg::Shutdown);
+        if let Some(h) = self.handle.take() {
+            let _ = h.join();
+        }
+        let snap = self.stats();
+        // A clean drain leaves in_flight == 0. A non-zero count here means the
+        // bounded drain bailed out on a hung device and leaked the ring+buffers
+        // to stay memory-safe (C4, rustfs/backlog#1055) — a degraded but safe
+        // outcome, not a panic. Callers/tests that require a clean drain assert
+        // on the returned snapshot themselves.
+        if snap.in_flight != 0 {
+            eprintln!(
+                "uring-spike shutdown: {} ops still in flight (bounded-drain bailout on a hung device)",
+                snap.in_flight
+            );
+        }
+        snap
+    }
+}
+
+impl Drop for UringDriver {
+    fn drop(&mut self) {
+        if let Some(h) = self.handle.take() {
+            let _ = self.tx.send(Msg::Shutdown);
+            let _ = h.join();
+        }
+    }
+}
+
+fn probe_real_read(ring: &mut IoUring) -> io::Result<()> {
+    let pattern: Vec<u8> = (0..512u32).map(|i| (i * 7 + 13) as u8).collect();
+
+    // Open an anonymous probe file seeded with the pattern. File setup runs
+    // BEFORE any SQE, so its errors early-return safely — nothing is in flight.
+    let file = open_probe_file(&pattern)?;
+
+    let mut buf = vec![0u8; pattern.len()];
+    let sqe = opcode::Read::new(types::Fd(file.as_raw_fd()), buf.as_mut_ptr(), buf.len() as u32)
+        .offset(0)
+        .build()
+        .user_data(0xB0BE);
+
+    // SAFETY: a push failure means the kernel never accepted the SQE, so
+    // `buf`/`file` may be dropped safely on this early return.
+    if unsafe { ring.submission().push(&sqe) }.is_err() {
+        return Err(io::Error::other("probe: submission queue full"));
+    }
+
+    // C1 (rustfs/backlog#1053): once the SQE is handed to the kernel, the read
+    // may be punted to io-wq and write into `buf` at ANY later point. Until its
+    // CQE arrives, `buf`/`file` must NOT be dropped and the ring must NOT be
+    // unmapped — otherwise the kernel writes into freed memory (UAF). The probe
+    // path has no pending-table backstop, so we must drain to the CQE here, and
+    // any early exit first leaks the buffer ("leak over UAF").
+    let res = match drain_probe_cqe(ring) {
+        Ok(res) => res,
+        Err(e) => {
+            // Could not confirm the op terminated: leak `buf` (the real UAF
+            // hazard — the kernel may still write 512 bytes into it) and,
+            // defensively, `file`. Leaking one 512-byte startup-probe buffer is
+            // trivially cheaper than a silent heap corruption.
+            std::mem::forget(buf);
+            std::mem::forget(file);
+            return Err(e);
+        }
+    };
+
+    // The CQE has arrived: the kernel is done with `buf`, so dropping it and
+    // `file` below is now safe.
+    if res < 0 {
+        Err(io::Error::from_raw_os_error(-res))
+    } else if res as usize != pattern.len() || buf != pattern {
+        Err(io::Error::other("probe: read completed but data mismatched"))
+    } else {
+        Ok(())
+    }
+}
+
+/// Open a probe file seeded with `pattern`, avoiding the symlink/TOCTOU/
+/// leftover hazards of a predictable temp path (C3, rustfs/backlog#1061).
+///
+/// Primary: `O_TMPFILE` — an anonymous inode with no name at all, so there is
+/// nothing for an attacker to pre-plant a symlink at, no TOCTOU window, and no
+/// leftover file. Fallback (filesystems without O_TMPFILE): create in the temp
+/// dir with `O_CREAT|O_EXCL|O_NOFOLLOW` + 0600 + a per-process nonce, then
+/// unlink immediately so no attacker-planted symlink is followed and no named
+/// file survives.
+fn open_probe_file(pattern: &[u8]) -> io::Result<File> {
+    let dir = std::env::temp_dir();
+    let c_dir = std::ffi::CString::new(dir.as_os_str().as_bytes()).map_err(|_| io::Error::other("probe dir path has NUL"))?;
+    // SAFETY: `c_dir` is a valid NUL-terminated path; O_TMPFILE requires a
+    // directory and O_RDWR/O_WRONLY. On success we own the returned fd.
+    let fd = unsafe { libc::open(c_dir.as_ptr(), libc::O_TMPFILE | libc::O_RDWR | libc::O_CLOEXEC, 0o600) };
+    if fd >= 0 {
+        let mut file = unsafe { File::from_raw_fd(fd) };
+        file.write_all(pattern)?;
+        return Ok(file);
+    }
+    open_probe_file_exclusive(&dir, pattern)
+}
+
+fn open_probe_file_exclusive(dir: &std::path::Path, pattern: &[u8]) -> io::Result<File> {
+    static SEQ: AtomicU64 = AtomicU64::new(0);
+    let nonce = SEQ.fetch_add(1, Ordering::Relaxed);
+    let path = dir.join(format!("uring-spike-probe-{}-{}", std::process::id(), nonce));
+    let c_path = std::ffi::CString::new(path.as_os_str().as_bytes()).map_err(|_| io::Error::other("probe path has NUL"))?;
+    // O_EXCL refuses a pre-existing file; O_NOFOLLOW refuses a symlink; 0600 is
+    // owner-only. SAFETY: `c_path` is a valid NUL-terminated path; on success
+    // we own the fd.
+    let fd = unsafe {
+        libc::open(
+            c_path.as_ptr(),
+            libc::O_CREAT | libc::O_EXCL | libc::O_NOFOLLOW | libc::O_RDWR | libc::O_CLOEXEC,
+            0o600,
+        )
+    };
+    if fd < 0 {
+        return Err(io::Error::last_os_error());
+    }
+    let mut file = unsafe { File::from_raw_fd(fd) };
+    file.write_all(pattern)?;
+    // Unlink now: the fd stays valid, no named leftover remains.
+    // SAFETY: `c_path` is still a valid NUL-terminated path.
+    unsafe {
+        libc::unlink(c_path.as_ptr());
+    }
+    Ok(file)
+}
+
+/// Wait for the probe SQE's CQE and return its raw result.
+///
+/// The SQE has already been pushed; this only drains it. `submit_and_wait`
+/// interrupted by a signal returns EINTR — since the kernel consumed the SQE
+/// atomically before the wait phase, we retry the WAIT only and never re-push
+/// (C8, backlog#1059). A bounded attempt count keeps a probe that hit a hung
+/// device from blocking forever; exhausting it returns an error that drives
+/// the caller's leak-over-UAF fallback.
+fn drain_probe_cqe(ring: &mut IoUring) -> io::Result<i32> {
+    const MAX_WAIT_ATTEMPTS: u32 = 4096;
+    for _ in 0..MAX_WAIT_ATTEMPTS {
+        match ring.submit_and_wait(1) {
+            Ok(_) => {}
+            // Signal interrupted the wait; the SQE is already in flight, so
+            // just wait again (do NOT re-push).
+            Err(e) if e.raw_os_error() == Some(libc::EINTR) => {}
+            Err(e) => return Err(e),
+        }
+        if let Some(cqe) = ring.completion().next() {
+            return Ok(cqe.result());
+        }
+    }
+    Err(io::Error::other("probe: no CQE after bounded wait"))
+}
+
+/// Owns everything the kernel can still be writing into: the ring, the
+/// pending (orphan) table of in-flight buffers, and the SQE backlog.
+///
+/// C2 (rustfs/backlog#1054): the "CQE is the only reclamation point"
+/// invariant holds only while the driver thread does NOT unwind. On a panic,
+/// Rust would drop the pending table (freeing every in-flight buffer) while
+/// the kernel may still write into them → mass UAF; reversing drop order does
+/// not help because io_uring teardown on ring drop is asynchronous and does
+/// not wait for in-flight ops. So this type's `Drop` refuses to run field
+/// destructors during an unwind: it aborts the process first, leaving the
+/// ring mapped and the buffers allocated (leak over UAF). A storage read path
+/// silently corrupting memory is worse than a crash.
+struct DriverState {
+    ring: IoUring,
+    pending: HashMap<u64, Pending>,
+    backlog: VecDeque<io_uring::squeue::Entry>,
+}
+
+impl Drop for DriverState {
+    fn drop(&mut self) {
+        if std::thread::panicking() {
+            // Abort BEFORE any field destructor runs: the ring stays mapped
+            // and the in-flight buffers stay allocated, so the kernel can
+            // never write into freed memory.
+            eprintln!(
+                "uring-spike driver thread panicked with {} ops in flight; \
+                 aborting to avoid UAF of in-flight buffers",
+                self.pending.len()
+            );
+            std::process::abort();
+        }
+        // Normal drop: the shutdown invariant guarantees pending/backlog are
+        // empty and in_flight == 0, so unmapping the ring here is safe.
+    }
+}
+
+/// What to do with a pending entry after its CQE (C9, rustfs/backlog#1058).
+enum ReapStep {
+    /// The logical read is done: remove the entry and deliver this result.
+    Finish(io::Result<Vec<u8>>),
+    /// Short read, not EOF: re-queue this SQE for the remainder; keep the entry.
+    Resubmit(io_uring::squeue::Entry),
+}
+
+fn drive(ring: IoUring, rx: mpsc::Receiver<Msg>, stats: Arc<DriverStats>, bp: Arc<Backpressure>) {
+    let mut state = DriverState {
+        ring,
+        pending: HashMap::new(),
+        backlog: VecDeque::new(),
+    };
+    let mut shutting_down = false;
+    let mut drain_deadline: Option<Instant> = None;
+
+    loop {
+        // 1. Intake. Block (with timeout) only when fully idle; once ops are
+        //    in flight we must keep reaping, so only try_recv.
+        loop {
+            let idle = state.pending.is_empty() && state.backlog.is_empty() && !shutting_down;
+            let msg = if idle {
+                match rx.recv_timeout(Duration::from_millis(50)) {
+                    Ok(m) => m,
+                    Err(RecvTimeoutError::Timeout) => break,
+                    Err(RecvTimeoutError::Disconnected) => {
+                        shutting_down = true;
+                        break;
+                    }
+                }
+            } else {
+                match rx.try_recv() {
+                    Ok(m) => m,
+                    Err(TryRecvError::Empty) => break,
+                    Err(TryRecvError::Disconnected) => {
+                        shutting_down = true;
+                        break;
+                    }
+                }
+            };
+            match msg {
+                Msg::Read {
+                    id,
+                    file,
+                    offset,
+                    len,
+                    done,
+                } => {
+                    if shutting_down {
+                        let _ = done.send(Err(io::Error::other("uring driver shutting down")));
+                        // The op never became in-flight; return its permit.
+                        bp.release();
+                        continue;
+                    }
+                    let mut buf = vec![0u8; len];
+                    // The raw pointer is captured before `buf` moves into the
+                    // table; moving the Vec never relocates its heap block,
+                    // and the entry is only removed at the CQE. `len as u32`
+                    // is lossless: `submit` rejected anything > MAX_READ_LEN.
+                    let sqe = opcode::Read::new(types::Fd(file.as_raw_fd()), buf.as_mut_ptr(), len as u32)
+                        .offset(offset)
+                        .build()
+                        .user_data(id);
+                    state.pending.insert(
+                        id,
+                        Pending {
+                            buf,
+                            file,
+                            done: Some(done),
+                            offset,
+                            nread: 0,
+                        },
+                    );
+                    stats.submitted.fetch_add(1, Ordering::SeqCst);
+                    stats.in_flight.fetch_add(1, Ordering::SeqCst);
+                    state.backlog.push_back(sqe);
+                }
+                Msg::Cancel { id } => {
+                    if state.pending.contains_key(&id) {
+                        state
+                            .backlog
+                            .push_back(opcode::AsyncCancel::new(id).build().user_data(id | CANCEL_BIT));
+                    }
+                }
+                Msg::Shutdown => {
+                    shutting_down = true;
+                    for id in state.pending.keys() {
+                        state
+                            .backlog
+                            .push_back(opcode::AsyncCancel::new(*id).build().user_data(*id | CANCEL_BIT));
+                    }
+                }
+            }
+        }
+
+        // 2. Push backlog into the SQ (stop when full; retry next turn).
+        {
+            let mut sq = state.ring.submission();
+            while let Some(sqe) = state.backlog.pop_front() {
+                // SAFETY: read SQEs point into `pending`-owned buffers that
+                // live until their CQE; cancel SQEs carry no pointers.
+                if unsafe { sq.push(&sqe) }.is_err() {
+                    state.backlog.push_front(sqe);
+                    break;
+                }
+            }
+        }
+        match state.ring.submit() {
+            Ok(_) => {}
+            Err(e) if e.raw_os_error() == Some(libc::EBUSY) => {
+                // CQ-overflow backpressure on pre-5.19 NODROP kernels: the
+                // kernel refuses new submissions until we reap. Keep the
+                // backlog and reap this turn instead of spinning (C5,
+                // rustfs/backlog#1056).
+            }
+            Err(_) => {
+                // EINTR and friends: retry on the next loop turn.
+            }
+        }
+
+        // 3. Reap. A Pending entry (and thus its buffer) is dropped ONLY when
+        //    the logical read finishes; a short read is resubmitted for the
+        //    remainder and the entry stays put (C9, rustfs/backlog#1058).
+        while let Some(cqe) = state.ring.completion().next() {
+            let ud = cqe.user_data();
+            if ud & CANCEL_BIT != 0 {
+                // Result of the AsyncCancel op itself; the read's own CQE
+                // (ECANCELED or success) still arrives separately. Record the
+                // three-state outcome for diagnosability (C4,
+                // rustfs/backlog#1055): EALREADY means the read is executing
+                // and cannot be interrupted, i.e. its CQE may never come on a
+                // hung device — the signal the bounded drain below relies on.
+                match cqe.result() {
+                    0 => stats.cancel_succeeded.fetch_add(1, Ordering::SeqCst),
+                    r if r == -libc::ENOENT => stats.cancel_not_found.fetch_add(1, Ordering::SeqCst),
+                    r if r == -libc::EALREADY => stats.cancel_already.fetch_add(1, Ordering::SeqCst),
+                    _ => 0,
+                };
+                continue;
+            }
+            let res = cqe.result();
+            if !state.pending.contains_key(&ud) {
+                continue;
+            }
+
+            // Decide the next step while borrowing the entry, then act after
+            // the borrow ends (finish removes it; resubmit re-queues an SQE).
+            let step = {
+                let p = state.pending.get_mut(&ud).expect("checked above");
+                if res < 0 {
+                    // Error (incl. ECANCELED) terminates the logical read.
+                    ReapStep::Finish(Err(io::Error::from_raw_os_error(-res)))
+                } else if res == 0 {
+                    // Real EOF: deliver what was read so far.
+                    p.buf.truncate(p.nread);
+                    ReapStep::Finish(Ok(std::mem::take(&mut p.buf)))
+                } else {
+                    p.nread += res as usize;
+                    // Only POSITIONED reads (read_at, whole-range pread
+                    // contract) resubmit a short read. CURRENT_POSITION reads
+                    // (read_current on pipes/streams) follow read(2) semantics:
+                    // a short read is a valid final result and must be
+                    // delivered as-is — resubmitting would block forever
+                    // waiting for stream data that may never come.
+                    let is_stream = p.offset == CURRENT_POSITION;
+                    if is_stream || p.nread >= p.buf.len() {
+                        p.buf.truncate(p.nread);
+                        ReapStep::Finish(Ok(std::mem::take(&mut p.buf)))
+                    } else {
+                        // Positioned short read, not EOF: resubmit the
+                        // remainder into buf[nread..]. The buffer stays owned by
+                        // the driver and in_flight is unchanged — one logical op.
+                        let remaining = p.buf.len() - p.nread;
+                        // SAFETY: buf[nread..] is in bounds (nread < len) and
+                        // stays alive in the pending table until the CQE.
+                        let ptr = unsafe { p.buf.as_mut_ptr().add(p.nread) };
+                        let next_off = if p.offset == CURRENT_POSITION {
+                            CURRENT_POSITION
+                        } else {
+                            p.offset + p.nread as u64
+                        };
+                        let sqe = opcode::Read::new(types::Fd(p.file.as_raw_fd()), ptr, remaining as u32)
+                            .offset(next_off)
+                            .build()
+                            .user_data(ud);
+                        ReapStep::Resubmit(sqe)
+                    }
+                }
+            };
+
+            match step {
+                ReapStep::Finish(outcome) => {
+                    // Content hygiene (C12, rustfs/backlog#1062): the delivered
+                    // bytes are ⊆ [0, res) — buf was freshly zeroed per op and
+                    // truncated to res. When P3 reuses a driver-owned slab
+                    // across requests, this ⊆ [0, res) property MUST be
+                    // preserved or a previous tenant's object bytes leak.
+                    let mut p = state.pending.remove(&ud).expect("checked above");
+                    match p.done.take().expect("done sender set at submit").send(outcome) {
+                        Ok(()) => stats.delivered.fetch_add(1, Ordering::SeqCst),
+                        // Caller dropped the future: the buffer survived in
+                        // the table until this final CQE and is reclaimed here.
+                        Err(_) => stats.orphan_reclaimed.fetch_add(1, Ordering::SeqCst),
+                    };
+                    stats.in_flight.fetch_sub(1, Ordering::SeqCst);
+                    // Release the permit HERE, at the CQE (pending removed),
+                    // not at future drop (C10, rustfs/backlog#1060).
+                    bp.release();
+                }
+                ReapStep::Resubmit(sqe) => state.backlog.push_back(sqe),
+            }
+        }
+
+        // Monitor CQ overflow. With NODROP (asserted at probe) the crate's
+        // submit() auto-flushes the kernel overflow list, so this should stay
+        // 0; any non-zero value means CQEs were lost — pending entries would
+        // never be reclaimed. Record it as a fatal signal (C5,
+        // rustfs/backlog#1056).
+        let overflow = state.ring.completion().overflow();
+        if overflow != 0 {
+            stats.cq_overflow.store(overflow as u64, Ordering::SeqCst);
+            eprintln!("uring-spike driver: CQ overflow = {overflow}; CQEs lost — treat as fatal in P2");
+        }
+
+        // 4. Exit when drained: the kernel no longer references any buffer, so
+        //    dropping the ring (unmap) is safe. If a hung device keeps a CQE
+        //    from ever arriving, bail out under a bounded deadline instead of
+        //    blocking forever (C4, rustfs/backlog#1055).
+        if shutting_down {
+            if state.pending.is_empty() && state.backlog.is_empty() {
+                bp.shutdown(); // unblock any submit() waiter before we exit
+                return; // clean drain: DriverState drops normally, ring unmaps.
+            }
+            let deadline = *drain_deadline.get_or_insert_with(|| Instant::now() + DRAIN_TIMEOUT);
+            if Instant::now() >= deadline {
+                // A CQE may never arrive (ASYNC_CANCEL cannot interrupt an
+                // in-execution regular-file read on a hung disk). We must NOT
+                // unmap the ring or free the still-in-flight buffers — leak the
+                // whole state (leak over UAF) and exit so shutdown() returns.
+                eprintln!(
+                    "uring-spike driver: bounded drain timed out with {} ops still in flight; \
+                     leaking ring + buffers to stay memory-safe",
+                    state.pending.len()
+                );
+                bp.shutdown(); // unblock any submit() waiter
+                std::mem::forget(state);
+                return;
+            }
+        }
+
+        // Spike-grade pacing: production replaces this poll with eventfd +
+        // tokio AsyncFd reaping (backlog#894).
+        if !state.pending.is_empty() {
+            std::thread::sleep(Duration::from_micros(200));
+        }
+    }
+}
diff --git a/experiments/io-uring-cancel-spike/src/lib.rs b/experiments/io-uring-cancel-spike/src/lib.rs
new file mode 100644
index 000000000..59909c5bf
--- /dev/null
+++ b/experiments/io-uring-cancel-spike/src/lib.rs
@@ -0,0 +1,37 @@
+// Copyright 2024 RustFS Team
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! Spike 0 for rustfs/backlog#894 (P2 io_uring read backend).
+//!
+//! Proves the cancel-safety ownership model before any production work:
+//!
+//! - The read buffer and the file handle are owned by the driver's pending
+//!   (orphan) table from SQE submission until the CQE arrives. The kernel may
+//!   write into the buffer at any point in that window, so nothing else is
+//!   allowed to free or move its heap allocation.
+//! - Dropping the caller-side future only abandons the *result*. It never
+//!   touches the buffer. Optionally it submits `IORING_OP_ASYNC_CANCEL` to
+//!   accelerate the CQE; reclamation still happens only at the CQE.
+//! - Driver shutdown cancels all in-flight ops and drains the ring to
+//!   `in_flight == 0` before the ring is dropped (unmapped).
+//!
+//! NOT production code: the driver thread uses a coarse poll loop instead of
+//! eventfd + `AsyncFd` reaping, there is no SQ-depth semaphore backpressure,
+//! no O_DIRECT alignment, and only one read shape. See SPIKE.md.
+
+#[cfg(target_os = "linux")]
+mod driver;
+
+#[cfg(target_os = "linux")]
+pub use driver::{ProbeFailure, StatsSnapshot, UringDriver};
diff --git a/experiments/io-uring-cancel-spike/tests/cancel.rs b/experiments/io-uring-cancel-spike/tests/cancel.rs
new file mode 100644
index 000000000..68612583b
--- /dev/null
+++ b/experiments/io-uring-cancel-spike/tests/cancel.rs
@@ -0,0 +1,472 @@
+// Copyright 2024 RustFS Team
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+//! Cancel-safety acceptance tests for backlog#894 Spike 0.
+//!
+//! In a restricted environment (Docker default seccomp, gVisor) the probe
+//! fails with an expected-restriction errno and every test degrades to a
+//! skip — the same contract P2's production probe must honor. Run under
+//! `--security-opt seccomp=unconfined` (see run-docker.sh) to exercise the
+//! real io_uring paths.
+#![cfg(target_os = "linux")]
+
+use std::fs::File;
+use std::io::Write;
+use std::os::fd::{AsRawFd, FromRawFd};
+use std::sync::Arc;
+use std::time::{Duration, Instant};
+
+use io_uring_cancel_spike::UringDriver;
+
+fn driver_or_skip(name: &str) -> Option<UringDriver> {
+    match UringDriver::probe_and_start(64) {
+        Ok(d) => Some(d),
+        Err(e) => {
+            assert!(
+                e.is_expected_restriction(),
+                "probe failed OUTSIDE the expected restriction errno class \
+                 (EACCES/EPERM/ENOSYS/EINVAL/EOPNOTSUPP): {e:?}"
+            );
+            eprintln!("SKIP {name}: restricted environment, graceful degradation path taken ({e:?})");
+            None
+        }
+    }
+}
+
+/// Deterministic pseudo-random content so reads are verifiable.
+fn make_content(len: usize) -> Vec<u8> {
+    let mut state: u64 = 0x2545F4914F6CDD1D;
+    (0..len)
+        .map(|_| {
+            state ^= state << 13;
+            state ^= state >> 7;
+            state ^= state << 17;
+            state as u8
+        })
+        .collect()
+}
+
+fn temp_file_with(content: &[u8], tag: &str) -> (std::path::PathBuf, Arc<File>) {
+    let path = std::env::temp_dir().join(format!("uring-spike-{tag}-{}", std::process::id()));
+    std::fs::write(&path, content).expect("write temp file");
+    let file = Arc::new(File::open(&path).expect("open temp file"));
+    (path, file)
+}
+
+/// An OS pipe whose read side never completes until we write — the only
+/// deterministic way to hold an op in flight across a future drop.
+fn os_pipe() -> (Arc<File>, File) {
+    let mut fds = [0i32; 2];
+    // SAFETY: fds is a valid out-array; on success both fds are owned here
+    // and immediately wrapped in File which takes over closing them.
+    let rc = unsafe { libc::pipe(fds.as_mut_ptr()) };
+    assert_eq!(rc, 0, "pipe(2) failed");
+    let read = unsafe { File::from_raw_fd(fds[0]) };
+    let write = unsafe { File::from_raw_fd(fds[1]) };
+    (Arc::new(read), write)
+}
+
+async fn wait_until(deadline: Duration, mut cond: impl FnMut() -> bool) -> bool {
+    let start = Instant::now();
+    while start.elapsed() < deadline {
+        if cond() {
+            return true;
+        }
+        tokio::time::sleep(Duration::from_millis(5)).await;
+    }
+    cond()
+}
+
+/// Baseline: completed reads return exactly what pread would.
+#[tokio::test(flavor = "multi_thread")]
+async fn read_matches_std() {
+    let Some(driver) = driver_or_skip("read_matches_std") else {
+        return;
+    };
+    const LEN: usize = 8 << 20;
+    let content = make_content(LEN);
+    let (path, file) = temp_file_with(&content, "correctness");
+
+    for i in 0..64usize {
+        let offset = (i * 131_071) % (LEN - 70_000);
+        let len = 1 + (i * 8_191) % 65_536;
+        let got = driver
+            .read_at(Arc::clone(&file), offset as u64, len)
+            .await
+            .expect("read failed");
+        assert_eq!(got, &content[offset..offset + len], "mismatch at offset {offset} len {len}");
+    }
+
+    let snap = driver.shutdown();
+    assert_eq!(snap.delivered, 64);
+    assert_eq!(snap.orphan_reclaimed, 0);
+    let _ = std::fs::remove_file(path);
+}
+
+/// THE core spike assertion: drop the future while the op is provably still
+/// in flight (blocked pipe read, no cancel submitted) and verify the buffer
+/// stays owned by the driver until the CQE finally arrives.
+#[tokio::test(flavor = "multi_thread")]
+async fn dropped_future_buffer_lives_until_cqe() {
+    let Some(driver) = driver_or_skip("dropped_future_buffer_lives_until_cqe") else {
+        return;
+    };
+    let (pipe_read, mut pipe_write) = os_pipe();
+
+    let handle = driver.read_current(Arc::clone(&pipe_read), 4096).without_cancel_on_drop();
+    assert!(
+        wait_until(Duration::from_secs(2), || driver.stats().in_flight == 1).await,
+        "read never reached in-flight state"
+    );
+
+    drop(handle);
+
+    // No cancel was submitted and the pipe is empty: the op MUST stay in
+    // flight and the buffer MUST NOT be reclaimed, no matter how long the
+    // future has been gone.
+    tokio::time::sleep(Duration::from_millis(300)).await;
+    let snap = driver.stats();
+    assert_eq!(snap.in_flight, 1, "op vanished without a CQE");
+    assert_eq!(snap.orphan_reclaimed, 0, "buffer reclaimed before CQE — UAF window!");
+
+    // Now let the kernel complete the read; the CQE both writes into the
+    // driver-owned buffer (safely) and triggers reclamation.
+    pipe_write.write_all(&[0xAB; 512]).expect("pipe write");
+    assert!(
+        wait_until(Duration::from_secs(2), || {
+            let s = driver.stats();
+            s.in_flight == 0 && s.orphan_reclaimed == 1
+        })
+        .await,
+        "orphaned op was not reclaimed at CQE: {:?}",
+        driver.stats()
+    );
+
+    driver.shutdown();
+}
+
+/// Default drop path: ASYNC_CANCEL accelerates the CQE so the orphaned
+/// buffer is reclaimed promptly without any data ever arriving.
+#[tokio::test(flavor = "multi_thread")]
+async fn async_cancel_accelerates_reclaim() {
+    let Some(driver) = driver_or_skip("async_cancel_accelerates_reclaim") else {
+        return;
+    };
+    let (pipe_read, pipe_write) = os_pipe();
+
+    let handle = driver.read_current(Arc::clone(&pipe_read), 4096);
+    assert!(
+        wait_until(Duration::from_secs(2), || driver.stats().in_flight == 1).await,
+        "read never reached in-flight state"
+    );
+
+    drop(handle); // submits IORING_OP_ASYNC_CANCEL
+
+    assert!(
+        wait_until(Duration::from_secs(2), || {
+            let s = driver.stats();
+            s.in_flight == 0 && s.orphan_reclaimed == 1
+        })
+        .await,
+        "cancel did not reclaim the orphan: {:?}",
+        driver.stats()
+    );
+
+    drop(pipe_write);
+    driver.shutdown();
+}
+
+/// Volume test modeling the EC quorum pattern: many concurrent reads, half
+/// the futures dropped immediately. Every op must be accounted for as either
+/// delivered or orphan-reclaimed, and survivors must return correct bytes.
+#[tokio::test(flavor = "multi_thread")]
+async fn cancel_stress_accounts_for_every_buffer() {
+    let Some(driver) = driver_or_skip("cancel_stress_accounts_for_every_buffer") else {
+        return;
+    };
+    const LEN: usize = 8 << 20;
+    const OPS: usize = 256;
+    const READ_LEN: usize = 64 << 10;
+    let content = make_content(LEN);
+    let (path, file) = temp_file_with(&content, "stress");
+
+    let mut kept = Vec::new();
+    for i in 0..OPS {
+        let offset = (i * 97_611) % (LEN - READ_LEN);
+        let handle = driver.read_at(Arc::clone(&file), offset as u64, READ_LEN);
+        if i % 2 == 0 {
+            drop(handle); // dropped mid-flight or post-completion — both must be safe
+        } else {
+            kept.push((offset, handle));
+        }
+    }
+
+    for (offset, handle) in kept {
+        let got = handle.await.expect("kept read failed");
+        assert_eq!(got, &content[offset..offset + READ_LEN], "mismatch at offset {offset}");
+    }
+
+    let snap = driver.shutdown();
+    assert_eq!(snap.submitted, OPS as u64);
+    // The exact split delivered == OPS/2 was flaky (C18, rustfs/backlog#1066):
+    // an even-i read can finish between read_at returning and drop(handle),
+    // delivering to the still-live receiver and flipping the split — all while
+    // the ownership model behaves correctly. Only the conservation identity is
+    // deterministic; the kept half guarantees delivered >= OPS/2.
+    assert!(snap.delivered >= (OPS / 2) as u64, "kept half not all delivered: {snap:?}");
+    assert_eq!(
+        snap.delivered + snap.orphan_reclaimed,
+        OPS as u64,
+        "some buffers are unaccounted for: {snap:?}"
+    );
+    let _ = std::fs::remove_file(path);
+}
+
+/// Shutdown with ops still blocked in flight must cancel + drain them before
+/// the driver thread exits (and the ring is unmapped).
+#[tokio::test(flavor = "multi_thread")]
+async fn shutdown_drains_in_flight_ops() {
+    let Some(driver) = driver_or_skip("shutdown_drains_in_flight_ops") else {
+        return;
+    };
+    let (pipe_read, pipe_write) = os_pipe();
+
+    let h1 = driver.read_current(Arc::clone(&pipe_read), 1024);
+    let h2 = driver.read_current(Arc::clone(&pipe_read), 1024);
+    assert!(
+        wait_until(Duration::from_secs(2), || driver.stats().in_flight == 2).await,
+        "reads never reached in-flight state"
+    );
+
+    // shutdown() cancels both, drains to in_flight == 0 (asserted inside),
+    // and joins the thread. The held futures then resolve with ECANCELED.
+    let snap = driver.shutdown();
+    assert_eq!(snap.in_flight, 0);
+    assert_eq!(snap.delivered + snap.orphan_reclaimed, snap.submitted);
+
+    for h in [h1, h2] {
+        let err = h.await.expect_err("blocked pipe read cannot have succeeded");
+        assert_eq!(err.raw_os_error(), Some(libc::ECANCELED), "unexpected error: {err:?}");
+    }
+
+    drop(pipe_write);
+}
+
+/// Invariant 2 regression (C20, rustfs/backlog#1064): the pending table — not
+/// the caller — owns the fd. Deleting `Pending.file` used to leave every test
+/// green because each test kept its own Arc<File> alive; this pins it. Drop the
+/// caller's Arc while the op is in flight (bare drop, no cancel) and assert the
+/// fd is STILL open: only the pending table's clone keeps it alive. If that
+/// field were removed, the File would close the fd and F_GETFD returns EBADF.
+#[tokio::test(flavor = "multi_thread")]
+async fn pending_table_owns_fd_after_caller_drop() {
+    let Some(driver) = driver_or_skip("pending_table_owns_fd_after_caller_drop") else {
+        return;
+    };
+    let (pipe_read, mut pipe_write) = os_pipe();
+    let raw_fd = pipe_read.as_raw_fd();
+
+    let handle = driver.read_current(Arc::clone(&pipe_read), 64).without_cancel_on_drop();
+    assert!(
+        wait_until(Duration::from_secs(2), || driver.stats().in_flight == 1).await,
+        "read never reached in-flight state"
+    );
+
+    // The pending table is now the ONLY owner of the fd.
+    drop(handle);
+    drop(pipe_read);
+    tokio::time::sleep(Duration::from_millis(50)).await;
+
+    // SAFETY: F_GETFD only queries the descriptor; it neither closes nor
+    // mutates it.
+    let rc = unsafe { libc::fcntl(raw_fd, libc::F_GETFD) };
+    assert_ne!(
+        rc,
+        -1,
+        "fd was closed while an op is in flight — the pending table does not own it \
+         (invariant 2 unprotected): {}",
+        std::io::Error::last_os_error()
+    );
+
+    // Complete the op so the driver reclaims cleanly.
+    pipe_write.write_all(&[0x5A; 64]).expect("pipe write");
+    assert!(
+        wait_until(Duration::from_secs(2), || driver.stats().in_flight == 0).await,
+        "op was not reclaimed at CQE"
+    );
+    driver.shutdown();
+}
+
+/// Memory-safety integrity (C14, rustfs/backlog#1064): while an orphaned
+/// blocked-pipe read holds a driver-owned buffer in flight the whole time, many
+/// delivered reads must still come back byte-exact — the kernel writing into
+/// the orphan's still-owned buffer must not corrupt anything, and the orphan
+/// buffer must NOT be reclaimed before its own CQE. This is a direct
+/// data-integrity observation, not just a counter identity. (A driver-level
+/// poison/canary leg is a P2 acceptance-matrix item; ASAN cannot see a kernel
+/// write into a freed buffer, so it is not the mechanism.)
+#[tokio::test(flavor = "multi_thread")]
+async fn orphan_in_flight_does_not_corrupt_delivered_reads() {
+    let Some(driver) = driver_or_skip("orphan_in_flight_does_not_corrupt_delivered_reads") else {
+        return;
+    };
+    let (pipe_read, mut pipe_write) = os_pipe();
+    let orphan = driver.read_current(Arc::clone(&pipe_read), 4096).without_cancel_on_drop();
+    assert!(
+        wait_until(Duration::from_secs(2), || driver.stats().in_flight == 1).await,
+        "orphan never reached in-flight state"
+    );
+    drop(orphan); // bare drop: buffer stays owned by the driver until its CQE
+
+    const LEN: usize = 1 << 20;
+    let content = make_content(LEN);
+    let (path, file) = temp_file_with(&content, "canary");
+    for i in 0..64usize {
+        let offset = (i * 9_973) % (LEN - 4096);
+        let got = driver
+            .read_at(Arc::clone(&file), offset as u64, 4096)
+            .await
+            .expect("read failed");
+        assert_eq!(got, &content[offset..offset + 4096], "delivered read corrupted at offset {offset}");
+    }
+    assert_eq!(driver.stats().orphan_reclaimed, 0, "orphan buffer reclaimed before its CQE");
+
+    pipe_write.write_all(&[0u8; 512]).expect("pipe write");
+    driver.shutdown();
+    let _ = std::fs::remove_file(path);
+}
+
+/// CQ-overflow safety (C15, rustfs/backlog#1065). With backpressure capping
+/// in-flight at the SQ depth (64) below CQ capacity (128), overflow is
+/// structurally unreachable. Drive far more ops than CQ capacity through and
+/// assert the kernel overflow counter stays 0 and every op is delivered.
+#[tokio::test(flavor = "multi_thread")]
+async fn no_cq_overflow_under_load() {
+    let Some(driver) = driver_or_skip("no_cq_overflow_under_load") else {
+        return;
+    };
+    const LEN: usize = 8 << 20;
+    const OPS: usize = 300; // > CQ capacity (128) many times over
+    const READ_LEN: usize = 4096;
+    let content = make_content(LEN);
+    let (path, file) = temp_file_with(&content, "overflow");
+
+    let mut kept = Vec::new();
+    for i in 0..OPS {
+        let offset = (i * 4_093) % (LEN - READ_LEN);
+        kept.push((offset, driver.read_at(Arc::clone(&file), offset as u64, READ_LEN)));
+    }
+    for (offset, handle) in kept {
+        let got = handle.await.expect("read failed");
+        assert_eq!(got, &content[offset..offset + READ_LEN], "mismatch at offset {offset}");
+    }
+
+    let snap = driver.shutdown();
+    assert_eq!(snap.cq_overflow, 0, "CQ overflowed under load: {snap:?}");
+    assert_eq!(snap.delivered, OPS as u64);
+    let _ = std::fs::remove_file(path);
+}
+
+/// Boundary reads on a regular file (C16, rustfs/backlog#1065): len==0, read at
+/// EOF, a cross-EOF short read delivered to a live receiver (exercises the C9
+/// resubmit loop), and the rejected huge-len / huge-offset guards (C6/C7).
+#[tokio::test(flavor = "multi_thread")]
+async fn boundary_reads() {
+    let Some(driver) = driver_or_skip("boundary_reads") else {
+        return;
+    };
+    const LEN: usize = 4096;
+    let content = make_content(LEN);
+    let (path, file) = temp_file_with(&content, "boundary");
+
+    // len == 0 → empty Ok.
+    let got = driver.read_at(Arc::clone(&file), 0, 0).await.expect("len=0 read");
+    assert!(got.is_empty(), "len=0 should return empty, got {}", got.len());
+
+    // offset == file size → EOF → empty Ok.
+    let got = driver.read_at(Arc::clone(&file), LEN as u64, 128).await.expect("EOF read");
+    assert!(got.is_empty(), "read at EOF should be empty, got {}", got.len());
+
+    // Read spanning past EOF → the available tail bytes, delivered to a live
+    // receiver via the resubmit-then-EOF path.
+    let got = driver
+        .read_at(Arc::clone(&file), (LEN - 10) as u64, 100)
+        .await
+        .expect("cross-EOF read");
+    assert_eq!(got, &content[LEN - 10..LEN], "cross-EOF read should return the tail only");
+
+    // len > MAX_RW_COUNT → rejected (C6); offset > i64::MAX → rejected (C7).
+    let err = driver
+        .read_at(Arc::clone(&file), 0, (1usize << 32) + 1)
+        .await
+        .expect_err("huge len must be rejected");
+    assert_eq!(err.kind(), std::io::ErrorKind::InvalidInput, "huge len error: {err:?}");
+    let err = driver
+        .read_at(Arc::clone(&file), (i64::MAX as u64) + 1, 16)
+        .await
+        .expect_err("huge offset must be rejected");
+    assert_eq!(err.kind(), std::io::ErrorKind::InvalidInput, "huge offset error: {err:?}");
+
+    driver.shutdown();
+    let _ = std::fs::remove_file(path);
+}
+
+/// Pipe half-close boundary (C16, rustfs/backlog#1065): an in-flight read whose
+/// write end is closed observes EOF (res=0) and returns empty.
+#[tokio::test(flavor = "multi_thread")]
+async fn pipe_half_close_reads_eof() {
+    let Some(driver) = driver_or_skip("pipe_half_close_reads_eof") else {
+        return;
+    };
+    let (pipe_read, pipe_write) = os_pipe();
+    let handle = driver.read_current(Arc::clone(&pipe_read), 128);
+    assert!(
+        wait_until(Duration::from_secs(2), || driver.stats().in_flight == 1).await,
+        "read never reached in-flight state"
+    );
+    drop(pipe_write); // close write end → blocked read observes EOF
+    let got = handle.await.expect("pipe EOF read");
+    assert!(got.is_empty(), "closed-pipe read should be empty EOF, got {}", got.len());
+    driver.shutdown();
+}
+
+/// Drop-without-shutdown path (C17, rustfs/backlog#1066): every other test ends
+/// via explicit shutdown(), so the UringDriver `Drop` impl's live-thread branch
+/// was never exercised. Drop the driver directly with ops still in flight; the
+/// Drop must send Shutdown BEFORE joining (send-after-join would deadlock at
+/// recv), cancel + drain the in-flight ops, and join — the held futures then
+/// resolve to ECANCELED. A regression (join-first, or an unbounded hang) makes
+/// this test hang.
+#[tokio::test(flavor = "multi_thread")]
+async fn drop_without_shutdown_drains_and_cancels() {
+    let Some(driver) = driver_or_skip("drop_without_shutdown_drains_and_cancels") else {
+        return;
+    };
+    let (pipe_read, pipe_write) = os_pipe();
+    let h1 = driver.read_current(Arc::clone(&pipe_read), 1024);
+    let h2 = driver.read_current(Arc::clone(&pipe_read), 1024);
+    assert!(
+        wait_until(Duration::from_secs(2), || driver.stats().in_flight == 2).await,
+        "reads never reached in-flight state"
+    );
+
+    // No shutdown() — exercise Drop directly.
+    drop(driver);
+
+    for h in [h1, h2] {
+        let err = h.await.expect_err("blocked pipe read cannot have succeeded");
+        assert_eq!(err.raw_os_error(), Some(libc::ECANCELED), "unexpected error: {err:?}");
+    }
+    drop(pipe_write);
+}