Commit c0226eb8 authored by Minchan Kim's avatar Minchan Kim Committed by Linus Torvalds
Browse files

mm: fs: fix lru_cache_disabled race in bh_lru 

Check lru_cache_disabled under bh_lru_lock.  Otherwise, it could introduce
race below and it fails to migrate pages containing buffer_head.

   CPU 0					CPU 1

bh_lru_install
                                       lru_cache_disable
  lru_cache_disabled = false
                                       atomic_inc(&lru_disable_count);
				       invalidate_bh_lrus_cpu of CPU 0
				       bh_lru_lock
				       __invalidate_bh_lrus
				       bh_lru_unlock
  bh_lru_lock
  install the bh
  bh_lru_unlock

WHen this race happens a CMA allocation fails, which is critical for
the workload which depends on CMA.

Link: https://lkml.kernel.org/r/20220308180709.2017638-1-minchan@kernel.org


Fixes: 8cc621d2 ("mm: fs: invalidate BH LRU during page migration")
Signed-off-by: default avatarMinchan Kim <minchan@kernel.org>
Cc: Chris Goldsworthy <cgoldswo@codeaurora.org>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: John Dias <joaodias@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 854d8e36

fs/buffer.c

+5 −3
Original line number Diff line number Diff line
@@ -1235,16 +1235,18 @@ static void bh_lru_install(struct buffer_head *bh) 
	int i;



	check_irqs_on();

	bh_lru_lock();



	/*

	 * the refcount of buffer_head in bh_lru prevents dropping the

	 * attached page(i.e., try_to_free_buffers) so it could cause

	 * failing page migration.

	 * Skip putting upcoming bh into bh_lru until migration is done.

	 */

	if (lru_cache_disabled())

	if (lru_cache_disabled()) {

		bh_lru_unlock();

		return;



	bh_lru_lock();

	}



	b = this_cpu_ptr(&bh_lrus);

	for (i = 0; i < BH_LRU_SIZE; i++) {