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io_uring/io-wq: always retry worker create on ERESTART* 

If a task has a pending signal when create_io_thread() is called,
copy_process() will return -ERESTARTNOINTR. io_should_retry_thread()
will request a retry of create_io_thread() up to WORKER_INIT_LIMIT = 3
times. If all retries fail, the io_uring request will fail with
ECANCELED.
Commit 3918315c5dc ("io-wq: backoff when retrying worker creation")
added a linear backoff to allow the thread to handle its signal before
the retry. However, a thread receiving frequent signals may get unlucky
and have a signal pending at every retry. Since the userspace task
doesn't control when it receives signals, there's no easy way for it to
prevent the create_io_thread() failure due to pending signals. The task
may also lack the information necessary to regenerate the canceled SQE.
So always retry the create_io_thread() on the ERESTART* errors,
analogous to what a fork() syscall would do. EAGAIN can occur due to
various persistent conditions such as exceeding RLIMIT_NPROC, so respect
the WORKER_INIT_LIMIT retry limit for EAGAIN errors.

Signed-off-by: Caleb Sander Mateos <csander@purestorage.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
master
Caleb Sander Mateos 2025-12-02 13:57:44 -07:00 committed by Jens Axboe
parent 84230ad2d2
commit 34c78b8610
1 changed files with 3 additions and 2 deletions
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5
io_uring/io-wq.c
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@ -805,11 +805,12 @@ static inline bool io_should_retry_thread(struct io_worker *worker, long err)
*/
if (fatal_signal_pending(current))
return false;
if (worker->init_retries++ >= WORKER_INIT_LIMIT)
return false;
worker->init_retries++;
switch (err) {
case -EAGAIN:
return worker->init_retries <= WORKER_INIT_LIMIT;
/* Analogous to a fork() syscall, always retry on a restartable error */
case -ERESTARTSYS:
case -ERESTARTNOINTR:
case -ERESTARTNOHAND: