From: Qian Cai <cai@xxxxxx>
Subject: mm/mempool: fix a data race in mempool_free()
mempool_t pool.curr_nr could be accessed concurrently as noticed by
KCSAN,
BUG: KCSAN: data-race in mempool_free / remove_element
write to 0xffffffffa937638c of 4 bytes by task 6359 on cpu 113:
remove_element+0x4a/0x1c0
remove_element at mm/mempool.c:132
mempool_alloc+0x102/0x210
(inlined by) mempool_alloc at mm/mempool.c:399
bio_alloc_bioset+0x106/0x2c0
get_swap_bio+0x49/0x230
__swap_writepage+0x680/0xc30
swap_writepage+0x9c/0xf0
pageout+0x33e/0xae0
shrink_page_list+0x1f57/0x2870
shrink_inactive_list+0x316/0x880
shrink_lruvec+0x8dc/0x1380
shrink_node+0x317/0xd80
do_try_to_free_pages+0x1f7/0xa10
try_to_free_pages+0x26c/0x5e0
__alloc_pages_slowpath+0x458/0x1290
<snip>
read to 0xffffffffa937638c of 4 bytes by interrupt on cpu 64:
mempool_free+0x3e/0x150
mempool_free at mm/mempool.c:492
bio_free+0x192/0x280
bio_put+0x91/0xd0
end_swap_bio_write+0x1d8/0x280
bio_endio+0x2c2/0x5b0
dec_pending+0x22b/0x440 [dm_mod]
clone_endio+0xe4/0x2c0 [dm_mod]
bio_endio+0x2c2/0x5b0
blk_update_request+0x217/0x940
scsi_end_request+0x6b/0x4d0
scsi_io_completion+0xb7/0x7e0
scsi_finish_command+0x223/0x310
scsi_softirq_done+0x1d5/0x210
blk_mq_complete_request+0x224/0x250
scsi_mq_done+0xc2/0x250
pqi_raid_io_complete+0x5a/0x70 [smartpqi]
pqi_irq_handler+0x150/0x1410 [smartpqi]
__handle_irq_event_percpu+0x90/0x540
handle_irq_event_percpu+0x49/0xd0
handle_irq_event+0x85/0xca
handle_edge_irq+0x13f/0x3e0
do_IRQ+0x86/0x190
<snip>
Since the write is under pool->lock but the read is done as lockless.
Even though the commit 5b990546e334 ("mempool: fix and document
synchronization and memory barrier usage") introduced the smp_wmb() and
smp_rmb() pair to improve the situation, it is adequate to protect it
from data races which could lead to a logic bug, so fix it by adding
READ_ONCE() for the read.
Link: http://lkml.kernel.org/r/1581446384-2131-1-git-send-email-cai@xxxxxx
Signed-off-by: Qian Cai <cai@xxxxxx>
Cc: Marco Elver <elver@xxxxxxxxxx>
Cc: Tejun Heo <tj@xxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/mempool.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
--- a/mm/mempool.c~mm-mempool-fix-a-data-race-in-mempool_free
+++ a/mm/mempool.c
@@ -489,7 +489,7 @@ void mempool_free(void *element, mempool
* ensures that there will be frees which return elements to the
* pool waking up the waiters.
*/
- if (unlikely(pool->curr_nr < pool->min_nr)) {
+ if (unlikely(READ_ONCE(pool->curr_nr) < pool->min_nr)) {
spin_lock_irqsave(&pool->lock, flags);
if (likely(pool->curr_nr < pool->min_nr)) {
add_element(pool, element);
_
