From: Stefano Garzarella Date: Fri, 21 Feb 2020 15:42:16 +0000 (+0100) Subject: io_uring: prevent sq_thread from spinning when it should stop X-Git-Tag: v5.6-rc3~8^2~1 X-Git-Url: https://asedeno.scripts.mit.edu/gitweb/?a=commitdiff_plain;ds=sidebyside;h=7143b5ac5750f404ff3a594b34fdf3fc2f99f828;hp=929a3af90f0f4bd7132d83552c1a98c83f60ef7e;p=linux.git 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: 6c271ce2f1d5 ("io_uring: add submission polling") Signed-off-by: Stefano Garzarella Signed-off-by: Jens Axboe --- diff --git a/fs/io_uring.c b/fs/io_uring.c index 6e249aa97ba3..b43467b3a8dc 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -5142,6 +5142,18 @@ static int io_sq_thread(void *data) * to enter the kernel to reap and flush events. */ 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 * period, then let us spin without work before going @@ -5156,18 +5168,6 @@ static int io_sq_thread(void *data) 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, TASK_INTERRUPTIBLE);