On Thu, Feb 27, 2020 at 11:12 AM gregkh@linuxfoundation.org wrote:

The patch below does not apply to the 5.4-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.

Thanks, I'll send the backport for 5.4-stable tree.

Stefano

thanks,

greg k-h

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

From 7143b5ac5750f404ff3a594b34fdf3fc2f99f828 Mon Sep 17 00:00:00 2001 From: Stefano Garzarella sgarzare@redhat.com Date: Fri, 21 Feb 2020 16:42:16 +0100 Subject: [PATCH] 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 sgarzare@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk

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);