[PATCH 5.16 0086/1017] mm: fs: fix lru_cache_disabled race in bh_lru

Greg Kroah-Hartman
2022-04-05T11:07:18Z

From: Minchan Kim <minchan@kernel.org>

commit c0226eb8bde854e016a594a16f5c0d98aca426fa upstream.

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: 8cc621d2f45d ("mm: fs: invalidate BH LRU during page migration")
Signed-off-by: Minchan 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/buffer.c | 8 +++++---
1 file changed, 5 insertions(+), 3 deletions(-)

--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1235,16 +1235,18 @@ static void bh_lru_install(struct buffer
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++) {