On Thu 15-03-18 18:07:47, Kirill A. Shutemov wrote:
> deferred_split_scan() gets called from reclaim path. Waiting for page
> lock may lead to deadlock there.
>
> Replace lock_page() with trylock_page() and skip the page if we failed
> to lock it. We will get to the page on the next scan.
>
Fixes: 9a982250f773 ("thp: introduce deferred_split_huge_page()")
and maybe even Cc: stable as this can lead to deadlocks AFAICS.
Btw. other THP shrinker does suffer from the same problem and a deadlock
has been reported[1]. Thanks for Tetsuo to point that out [2].
[1] http://lkml.kernel.org/r/alpine.LRH.2.11.1801242349220.30642@xxxxxxxxxxxxxxxxx
[2] http://lkml.kernel.org/r/04bbbd39-a1c0-b84b-28a2-0a3876be1054@xxxxxxxxxxxxxxxxxxx
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Anyway feel free to add
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
to this patch but a deeper audit is due I suspect
> ---
> mm/huge_memory.c | 4 +++-
> 1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 87ab9b8f56b5..529cf36b7edb 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2783,11 +2783,13 @@ static unsigned long deferred_split_scan(struct shrinker *shrink,
>
> list_for_each_safe(pos, next, &list) {
> page = list_entry((void *)pos, struct page, mapping);
> - lock_page(page);
> + if (!trylock_page(page))
> + goto next;
> /* split_huge_page() removes page from list on success */
> if (!split_huge_page(page))
> split++;
> unlock_page(page);
> +next:
> put_page(page);
> }
>
> --
> 2.16.1
--
Michal Hocko
SUSE Labs
