[dm-devel] [PATCH] direct-io: use GFP_NOIO to avoid deadlock

[Junxiao Bi]

Hi Mikulas,

This seemed not issue on mainline, mutex in dm_bufio_shrink_count() had 
been removed from mainline.

Thanks,

Junxiao.

On 8/8/19 2:50 AM, Mikulas Patocka wrote:
> A deadlock with this stacktrace was observed.
>
> The obvious problem here is that in the call chain
> xfs_vm_direct_IO->__blockdev_direct_IO->do_blockdev_direct_IO->kmem_cache_alloc
> we do a GFP_KERNEL allocation while we are in a filesystem driver and in a
> block device driver.
>
> This patch changes the direct-io code to use GFP_NOIO.
>
> PID: 474    TASK: ffff8813e11f4600  CPU: 10  COMMAND: "kswapd0"
>     #0 [ffff8813dedfb938] __schedule at ffffffff8173f405
>     #1 [ffff8813dedfb990] schedule at ffffffff8173fa27
>     #2 [ffff8813dedfb9b0] schedule_timeout at ffffffff81742fec
>     #3 [ffff8813dedfba60] io_schedule_timeout at ffffffff8173f186
>     #4 [ffff8813dedfbaa0] bit_wait_io at ffffffff8174034f
>     #5 [ffff8813dedfbac0] __wait_on_bit at ffffffff8173fec8
>     #6 [ffff8813dedfbb10] out_of_line_wait_on_bit at ffffffff8173ff81
>     #7 [ffff8813dedfbb90] __make_buffer_clean at ffffffffa038736f [dm_bufio]
>     #8 [ffff8813dedfbbb0] __try_evict_buffer at ffffffffa0387bb8 [dm_bufio]
>     #9 [ffff8813dedfbbd0] dm_bufio_shrink_scan at ffffffffa0387cc3 [dm_bufio]
>    #10 [ffff8813dedfbc40] shrink_slab at ffffffff811a87ce
>    #11 [ffff8813dedfbd30] shrink_zone at ffffffff811ad778
>    #12 [ffff8813dedfbdc0] kswapd at ffffffff811ae92f
>    #13 [ffff8813dedfbec0] kthread at ffffffff810a8428
>    #14 [ffff8813dedfbf50] ret_from_fork at ffffffff81745242
>
>    PID: 14127  TASK: ffff881455749c00  CPU: 11  COMMAND: "loop1"
>     #0 [ffff88272f5af228] __schedule at ffffffff8173f405
>     #1 [ffff88272f5af280] schedule at ffffffff8173fa27
>     #2 [ffff88272f5af2a0] schedule_preempt_disabled at ffffffff8173fd5e
>     #3 [ffff88272f5af2b0] __mutex_lock_slowpath at ffffffff81741fb5
>     #4 [ffff88272f5af330] mutex_lock at ffffffff81742133
>     #5 [ffff88272f5af350] dm_bufio_shrink_count at ffffffffa03865f9 [dm_bufio]
>     #6 [ffff88272f5af380] shrink_slab at ffffffff811a86bd
>     #7 [ffff88272f5af470] shrink_zone at ffffffff811ad778
>     #8 [ffff88272f5af500] do_try_to_free_pages at ffffffff811adb34
>     #9 [ffff88272f5af590] try_to_free_pages at ffffffff811adef8
>    #10 [ffff88272f5af610] __alloc_pages_nodemask at ffffffff811a09c3
>    #11 [ffff88272f5af710] alloc_pages_current at ffffffff811e8b71
>    #12 [ffff88272f5af760] new_slab at ffffffff811f4523
>    #13 [ffff88272f5af7b0] __slab_alloc at ffffffff8173a1b5
>    #14 [ffff88272f5af880] kmem_cache_alloc at ffffffff811f484b
>    #15 [ffff88272f5af8d0] do_blockdev_direct_IO at ffffffff812535b3
>    #16 [ffff88272f5afb00] __blockdev_direct_IO at ffffffff81255dc3
>    #17 [ffff88272f5afb30] xfs_vm_direct_IO at ffffffffa01fe3fc [xfs]
>    #18 [ffff88272f5afb90] generic_file_read_iter at ffffffff81198994
>    #19 [ffff88272f5afc50] __dta_xfs_file_read_iter_2398 at ffffffffa020c970 [xfs]
>    #20 [ffff88272f5afcc0] lo_rw_aio at ffffffffa0377042 [loop]
>    #21 [ffff88272f5afd70] loop_queue_work at ffffffffa0377c3b [loop]
>    #22 [ffff88272f5afe60] kthread_worker_fn at ffffffff810a8a0c
>    #23 [ffff88272f5afec0] kthread at ffffffff810a8428
>    #24 [ffff88272f5aff50] ret_from_fork at ffffffff81745242
>
> Signed-off-by: Mikulas Patocka <mpatocka at redhat.com>
> Cc: stable at vger.kernel.org
>
> ---
>   fs/direct-io.c |    4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> Index: linux-2.6/fs/direct-io.c
> ===================================================================
> --- linux-2.6.orig/fs/direct-io.c	2019-08-02 08:51:56.000000000 +0200
> +++ linux-2.6/fs/direct-io.c	2019-08-08 11:22:18.000000000 +0200
> @@ -436,7 +436,7 @@ dio_bio_alloc(struct dio *dio, struct di
>   	 * bio_alloc() is guaranteed to return a bio when allowed to sleep and
>   	 * we request a valid number of vectors.
>   	 */
> -	bio = bio_alloc(GFP_KERNEL, nr_vecs);
> +	bio = bio_alloc(GFP_NOIO, nr_vecs);
>   
>   	bio_set_dev(bio, bdev);
>   	bio->bi_iter.bi_sector = first_sector;
> @@ -1197,7 +1197,7 @@ do_blockdev_direct_IO(struct kiocb *iocb
>   	if (iov_iter_rw(iter) == READ && !count)
>   		return 0;
>   
> -	dio = kmem_cache_alloc(dio_cache, GFP_KERNEL);
> +	dio = kmem_cache_alloc(dio_cache, GFP_NOIO);
>   	retval = -ENOMEM;
>   	if (!dio)
>   		goto out;