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^..

Possible dependencies:

0453aad676ff ("io_uring/io-wq: limit retrying worker initialisation") 8a565304927f ("io_uring/io-wq: Use set_bit() and test_bit() at worker->flags") eb47943f2238 ("io-wq: Drop struct io_wqe") dfd63baf892c ("io-wq: Move wq accounting to io_wq") da64d6db3bd3 ("io_uring: One wqe per wq") 01e68ce08a30 ("io_uring/io-wq: stop setting PF_NO_SETAFFINITY on io-wq workers")

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

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

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.172063414... Signed-off-by: Jens Axboe axboe@kernel.dk

diff --git a/io_uring/io-wq.c b/io_uring/io-wq.c index 913c92249522..f1e7c670add8 100644 --- a/io_uring/io-wq.c +++ b/io_uring/io-wq.c @@ -23,6 +23,7 @@ #include "io_uring.h"

#define WORKER_IDLE_TIMEOUT (5 * HZ) +#define WORKER_INIT_LIMIT 3

enum { IO_WORKER_F_UP = 0, /* up and active */ @@ -58,6 +59,7 @@ struct io_worker {

unsigned long create_state; struct callback_head create_work; + int init_retries;

union { struct rcu_head rcu; @@ -745,7 +747,7 @@ 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 @@ -753,6 +755,8 @@ 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: @@ -779,7 +783,7 @@ static void create_worker_cont(struct callback_head *cb) io_init_new_worker(wq, 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_wq_acct *acct = io_wq_get_acct(worker);

atomic_dec(&acct->nr_running); @@ -846,7 +850,7 @@ static bool create_io_worker(struct io_wq *wq, int index) tsk = create_io_thread(io_wq_worker, worker, NUMA_NO_NODE); if (!IS_ERR(tsk)) { io_init_new_worker(wq, 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 {