io_uring: prevent sq_thread from spinning when it should stop

commit 7143b5ac5750f404ff3a594b34fdf3fc2f99f828 upstream.

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 <sgarzare@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 4797acd11b86490f496f48e7ee49a512217627ea..ed9a551882cf38a674c61ca36d56227625d8f630 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2731,16 +2731,6 @@ static int io_sq_thread(void *data)
 
                to_submit = io_sqring_entries(ctx);
                if (!to_submit) {
-                       /*
-                        * We're polling. If we're within the defined idle
-                        * period, then let us spin without work before going
-                        * to sleep.
-                        */
-                       if (inflight || !time_after(jiffies, timeout)) {
-                               cond_resched();
-                               continue;
-                       }
-
                        /*
                         * Drop cur_mm before scheduling, we can't hold it for
                         * long periods (or over schedule()). Do this before
@@ -2753,6 +2743,16 @@ static int io_sq_thread(void *data)
                                cur_mm = NULL;
                        }
 
+                       /*
+                        * We're polling. If we're within the defined idle
+                        * period, then let us spin without work before going
+                        * to sleep.
+                        */
+                       if (inflight || !time_after(jiffies, timeout)) {
+                               cond_resched();
+                               continue;
+                       }
+
                        prepare_to_wait(&ctx->sqo_wait, &wait,
                                                TASK_INTERRUPTIBLE);