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io_uring: prevent sq_thread from spinning when it should stop 

This patch drops 'cur_mm' before calling cond_resched(), to prevent
the sq_thread from spinning even when the user process is finished.

Before this patch, if the user process ended without closing the
io_uring fd, the sq_thread continues to spin until the
'sq_thread_idle' timeout ends.

In the worst case where the 'sq_thread_idle' parameter is bigger than
INT_MAX, the sq_thread will spin forever.

Fixes: 6c271ce2f1 ("io_uring: add submission polling")
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Stefano Garzarella 2020-02-21 16:42:16 +01:00 committed by Jens Axboe
parent 929a3af90f
commit 7143b5ac57
1 changed files with 12 additions and 12 deletions
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24
fs/io_uring.c
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@ -5142,6 +5142,18 @@ static int io_sq_thread(void *data)
* to enter the kernel to reap and flush events. * to enter the kernel to reap and flush events.
*/ */
if (!to_submit || ret == -EBUSY) { if (!to_submit || ret == -EBUSY) {
/*
* Drop cur_mm before scheduling, we can't hold it for
* long periods (or over schedule()). Do this before
* adding ourselves to the waitqueue, as the unuse/drop
* may sleep.
*/
if (cur_mm) {
unuse_mm(cur_mm);
mmput(cur_mm);
cur_mm = NULL;
}
/* /*
* We're polling. If we're within the defined idle * We're polling. If we're within the defined idle
* period, then let us spin without work before going * period, then let us spin without work before going
@ -5156,18 +5168,6 @@ static int io_sq_thread(void *data)
continue; continue;
} }
/*
* Drop cur_mm before scheduling, we can't hold it for
* long periods (or over schedule()). Do this before
* adding ourselves to the waitqueue, as the unuse/drop
* may sleep.
*/
if (cur_mm) {
unuse_mm(cur_mm);
mmput(cur_mm);
cur_mm = NULL;
}
prepare_to_wait(&ctx->sqo_wait, &wait, prepare_to_wait(&ctx->sqo_wait, &wait,
TASK_INTERRUPTIBLE); TASK_INTERRUPTIBLE);