Re: FAILED: patch "[PATCH] io_uring/io-wq: limit retrying worker initialisation" failed to apply to 6.1-stable tree

[Jens Axboe <axboe@kernel.dk>]

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On 7/29/24 1:55 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 0453aad676ff99787124b9b3af4a5f59fbe808e2
> # <resolve conflicts, build, test, etc.>
> git commit -s
> git send-email --to '<stable@vger.kernel.org>' --in-reply-to '2024072923-bodacious-claw-442b@gregkh' --subject-prefix 'PATCH 6.1.y' HEAD^..

Here's a 6.1 variant.

-- 
Jens Axboe


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From 0453aad676ff99787124b9b3af4a5f59fbe808e2 Mon Sep 17 00:00:00 2001
From: Pavel Begunkov <asml.silence@gmail.com>
Date: Wed, 10 Jul 2024 18:58:17 +0100
Subject: [PATCH] io_uring/io-wq: limit retrying worker initialisation

commit 0453aad676ff99787124b9b3af4a5f59fbe808e2 upstream.

If io-wq worker creation fails, we retry it by queueing up a task_work.
tasK_work is needed because it should be done from the user process
context. The problem is that retries are not limited, and if queueing a
task_work is the reason for the failure, we might get into an infinite
loop.

It doesn't seem to happen now but it would with the following patch
executing task_work in the freezer's loop. For now, arbitrarily limit the
number of attempts to create a worker.

Cc: stable@vger.kernel.org
Fixes: 3146cba99aa28 ("io-wq: make worker creation resilient against signals")
Reported-by: Julian Orth <ju.orth@gmail.com>
Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Link: https://lore.kernel.org/r/8280436925db88448c7c85c6656edee1a43029ea.1720634146.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 io_uring/io-wq.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/io_uring/io-wq.c b/io_uring/io-wq.c
index 98ac9dbcec2f..04503118cdc1 100644
--- a/io_uring/io-wq.c
+++ b/io_uring/io-wq.c
@@ -22,6 +22,7 @@
 #include "io_uring.h"
 
 #define WORKER_IDLE_TIMEOUT	(5 * HZ)
+#define WORKER_INIT_LIMIT	3
 
 enum {
 	IO_WORKER_F_UP		= 1,	/* up and active */
@@ -58,6 +59,7 @@ struct io_worker {
 	unsigned long create_state;
 	struct callback_head create_work;
 	int create_index;
+	int init_retries;
 
 	union {
 		struct rcu_head rcu;
@@ -729,7 +731,7 @@ static bool io_wq_work_match_all(struct io_wq_work *work, void *data)
 	return true;
 }
 
-static inline bool io_should_retry_thread(long err)
+static inline bool io_should_retry_thread(struct io_worker *worker, long err)
 {
 	/*
 	 * Prevent perpetual task_work retry, if the task (or its group) is
@@ -737,6 +739,8 @@ static inline bool io_should_retry_thread(long err)
 	 */
 	if (fatal_signal_pending(current))
 		return false;
+	if (worker->init_retries++ >= WORKER_INIT_LIMIT)
+		return false;
 
 	switch (err) {
 	case -EAGAIN:
@@ -763,7 +767,7 @@ static void create_worker_cont(struct callback_head *cb)
 		io_init_new_worker(wqe, worker, tsk);
 		io_worker_release(worker);
 		return;
-	} else if (!io_should_retry_thread(PTR_ERR(tsk))) {
+	} else if (!io_should_retry_thread(worker, PTR_ERR(tsk))) {
 		struct io_wqe_acct *acct = io_wqe_get_acct(worker);
 
 		atomic_dec(&acct->nr_running);
@@ -830,7 +834,7 @@ static bool create_io_worker(struct io_wq *wq, struct io_wqe *wqe, int index)
 	tsk = create_io_thread(io_wqe_worker, worker, wqe->node);
 	if (!IS_ERR(tsk)) {
 		io_init_new_worker(wqe, worker, tsk);
-	} else if (!io_should_retry_thread(PTR_ERR(tsk))) {
+	} else if (!io_should_retry_thread(worker, PTR_ERR(tsk))) {
 		kfree(worker);
 		goto fail;
 	} else {