Re: FAILED: patch "[PATCH] io_uring: include dying ring in task_work "should cancel"" failed to apply to 6.1-stable tree

[Jens Axboe <axboe@kernel.dk>]

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On 9/21/25 6:32 AM, gregkh@linuxfoundation.org wrote:
> 
> The patch below does not apply to the 6.1-stable tree.
> If someone wants it applied there, or to any other stable or longterm
> tree, then please email the backport, including the original git commit
> id to <stable@vger.kernel.org>.
> 
> To reproduce the conflict and resubmit, you may use the following commands:
> 
> git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.1.y
> git checkout FETCH_HEAD
> git cherry-pick -x 3539b1467e94336d5854ebf976d9627bfb65d6c3
> # <resolve conflicts, build, test, etc.>
> git commit -s
> git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2025092128-embassy-flyable-e3fb@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

And 6.1-stable variants here.

-- 
Jens Axboe

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From d22d8c2d939d3570a22e01bd1aacc8c551302521 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Thu, 18 Sep 2025 10:21:14 -0600
Subject: [PATCH 2/2] io_uring: include dying ring in task_work "should cancel"
 state

Commit 3539b1467e94336d5854ebf976d9627bfb65d6c3 upstream.

When running task_work for an exiting task, rather than perform the
issue retry attempt, the task_work is canceled. However, this isn't
done for a ring that has been closed. This can lead to requests being
successfully completed post the ring being closed, which is somewhat
confusing and surprising to an application.

Rather than just check the task exit state, also include the ring
ref state in deciding whether or not to terminate a given request when
run from task_work.

Cc: stable@vger.kernel.org # 6.1+
Link: https://github.com/axboe/liburing/discussions/1459
Reported-by: Benedek Thaler <thaler@thaler.hu>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 io_uring/io_uring.c | 12 ++++++++----
 io_uring/io_uring.h |  4 ++--
 io_uring/poll.c     |  2 +-
 io_uring/timeout.c  |  2 +-
 4 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index fa0c9c044931..2aae0de6169c 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -1248,8 +1248,10 @@ static void io_req_task_cancel(struct io_kiocb *req, bool *locked)
 
 void io_req_task_submit(struct io_kiocb *req, bool *locked)
 {
-	io_tw_lock(req->ctx, locked);
-	if (likely(!io_should_terminate_tw()))
+	struct io_ring_ctx *ctx = req->ctx;
+
+	io_tw_lock(ctx, locked);
+	if (likely(!io_should_terminate_tw(ctx)))
 		io_queue_sqe(req);
 	else
 		io_req_complete_failed(req, -EFAULT);
@@ -1771,8 +1773,10 @@ static int io_issue_sqe(struct io_kiocb *req, unsigned int issue_flags)
 
 int io_poll_issue(struct io_kiocb *req, bool *locked)
 {
-	io_tw_lock(req->ctx, locked);
-	if (unlikely(io_should_terminate_tw()))
+	struct io_ring_ctx *ctx = req->ctx;
+
+	io_tw_lock(ctx, locked);
+	if (unlikely(io_should_terminate_tw(ctx)))
 		return -EFAULT;
 	return io_issue_sqe(req, IO_URING_F_NONBLOCK|IO_URING_F_MULTISHOT);
 }
diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
index 37ef84520be4..194e3230f853 100644
--- a/io_uring/io_uring.h
+++ b/io_uring/io_uring.h
@@ -403,9 +403,9 @@ static inline bool io_allowed_run_tw(struct io_ring_ctx *ctx)
  * 2) PF_KTHREAD is set, in which case the invoker of the task_work is
  *    our fallback task_work.
  */
-static inline bool io_should_terminate_tw(void)
+static inline bool io_should_terminate_tw(struct io_ring_ctx *ctx)
 {
-	return current->flags & (PF_KTHREAD | PF_EXITING);
+	return (current->flags & (PF_KTHREAD | PF_EXITING)) || percpu_ref_is_dying(&ctx->refs);
 }
 
 static inline void io_req_queue_tw_complete(struct io_kiocb *req, s32 res)
diff --git a/io_uring/poll.c b/io_uring/poll.c
index a0152bdc1c61..e9f83d3fc835 100644
--- a/io_uring/poll.c
+++ b/io_uring/poll.c
@@ -241,7 +241,7 @@ static int io_poll_check_events(struct io_kiocb *req, bool *locked)
 	struct io_ring_ctx *ctx = req->ctx;
 	int v;
 
-	if (unlikely(io_should_terminate_tw()))
+	if (unlikely(io_should_terminate_tw(ctx)))
 		return -ECANCELED;
 
 	do {
diff --git a/io_uring/timeout.c b/io_uring/timeout.c
index 57fe63faa6ba..0bfd111e9164 100644
--- a/io_uring/timeout.c
+++ b/io_uring/timeout.c
@@ -275,7 +275,7 @@ static void io_req_task_link_timeout(struct io_kiocb *req, bool *locked)
 	int ret = -ENOENT;
 
 	if (prev) {
-		if (!io_should_terminate_tw()) {
+		if (!io_should_terminate_tw(req->ctx)) {
 			struct io_cancel_data cd = {
 				.ctx		= req->ctx,
 				.data		= prev->cqe.user_data,
-- 
2.51.0


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From 6a6e675da9217d775386a00cdb61347f3babeeec Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Thu, 18 Sep 2025 11:27:06 -0600
Subject: [PATCH 1/2] io_uring: backport io_should_terminate_tw()

Parts of commit b6f58a3f4aa8dba424356c7a69388a81f4459300 upstream.

Backport io_should_terminate_tw() helper to judge whether task_work
should be run or terminated.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 io_uring/io_uring.c |  5 ++---
 io_uring/io_uring.h | 13 +++++++++++++
 io_uring/poll.c     |  3 +--
 io_uring/timeout.c  |  2 +-
 4 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 29adfc6d6ec2..fa0c9c044931 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -1249,8 +1249,7 @@ static void io_req_task_cancel(struct io_kiocb *req, bool *locked)
 void io_req_task_submit(struct io_kiocb *req, bool *locked)
 {
 	io_tw_lock(req->ctx, locked);
-	/* req->task == current here, checking PF_EXITING is safe */
-	if (likely(!(req->task->flags & PF_EXITING)))
+	if (likely(!io_should_terminate_tw()))
 		io_queue_sqe(req);
 	else
 		io_req_complete_failed(req, -EFAULT);
@@ -1773,7 +1772,7 @@ static int io_issue_sqe(struct io_kiocb *req, unsigned int issue_flags)
 int io_poll_issue(struct io_kiocb *req, bool *locked)
 {
 	io_tw_lock(req->ctx, locked);
-	if (unlikely(req->task->flags & PF_EXITING))
+	if (unlikely(io_should_terminate_tw()))
 		return -EFAULT;
 	return io_issue_sqe(req, IO_URING_F_NONBLOCK|IO_URING_F_MULTISHOT);
 }
diff --git a/io_uring/io_uring.h b/io_uring/io_uring.h
index 886921d2d58d..37ef84520be4 100644
--- a/io_uring/io_uring.h
+++ b/io_uring/io_uring.h
@@ -395,6 +395,19 @@ static inline bool io_allowed_run_tw(struct io_ring_ctx *ctx)
 		      ctx->submitter_task == current);
 }
 
+/*
+ * Terminate the request if either of these conditions are true:
+ *
+ * 1) It's being executed by the original task, but that task is marked
+ *    with PF_EXITING as it's exiting.
+ * 2) PF_KTHREAD is set, in which case the invoker of the task_work is
+ *    our fallback task_work.
+ */
+static inline bool io_should_terminate_tw(void)
+{
+	return current->flags & (PF_KTHREAD | PF_EXITING);
+}
+
 static inline void io_req_queue_tw_complete(struct io_kiocb *req, s32 res)
 {
 	io_req_set_res(req, res, 0);
diff --git a/io_uring/poll.c b/io_uring/poll.c
index ab27a627fd4c..a0152bdc1c61 100644
--- a/io_uring/poll.c
+++ b/io_uring/poll.c
@@ -241,8 +241,7 @@ static int io_poll_check_events(struct io_kiocb *req, bool *locked)
 	struct io_ring_ctx *ctx = req->ctx;
 	int v;
 
-	/* req->task == current here, checking PF_EXITING is safe */
-	if (unlikely(req->task->flags & PF_EXITING))
+	if (unlikely(io_should_terminate_tw()))
 		return -ECANCELED;
 
 	do {
diff --git a/io_uring/timeout.c b/io_uring/timeout.c
index 7cdc234c5f53..57fe63faa6ba 100644
--- a/io_uring/timeout.c
+++ b/io_uring/timeout.c
@@ -275,7 +275,7 @@ static void io_req_task_link_timeout(struct io_kiocb *req, bool *locked)
 	int ret = -ENOENT;
 
 	if (prev) {
-		if (!(req->task->flags & PF_EXITING)) {
+		if (!io_should_terminate_tw()) {
 			struct io_cancel_data cd = {
 				.ctx		= req->ctx,
 				.data		= prev->cqe.user_data,
-- 
2.51.0