This is a note to let you know that I've just added the patch titled
mm/swap_state: fix a data race in swapin_nr_pages
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
mm-swap_state-fix-a-data-race-in-swapin_nr_pages.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 95250e7b7176b217f0796251f2aa89072a949da9
Author: Qian Cai <cai@xxxxxx>
Date: Mon Jun 1 21:48:40 2020 -0700
mm/swap_state: fix a data race in swapin_nr_pages
[ Upstream commit d6c1f098f2a7ba62627c9bc17cda28f534ef9e4a ]
"prev_offset" is a static variable in swapin_nr_pages() that can be
accessed concurrently with only mmap_sem held in read mode as noticed by
KCSAN,
BUG: KCSAN: data-race in swap_cluster_readahead / swap_cluster_readahead
write to 0xffffffff92763830 of 8 bytes by task 14795 on cpu 17:
swap_cluster_readahead+0x2a6/0x5e0
swapin_readahead+0x92/0x8dc
do_swap_page+0x49b/0xf20
__handle_mm_fault+0xcfb/0xd70
handle_mm_fault+0xfc/0x2f0
do_page_fault+0x263/0x715
page_fault+0x34/0x40
1 lock held by (dnf)/14795:
#0: ffff897bd2e98858 (&mm->mmap_sem#2){++++}-{3:3}, at: do_page_fault+0x143/0x715
do_user_addr_fault at arch/x86/mm/fault.c:1405
(inlined by) do_page_fault at arch/x86/mm/fault.c:1535
irq event stamp: 83493
count_memcg_event_mm+0x1a6/0x270
count_memcg_event_mm+0x119/0x270
__do_softirq+0x365/0x589
irq_exit+0xa2/0xc0
read to 0xffffffff92763830 of 8 bytes by task 1 on cpu 22:
swap_cluster_readahead+0xfd/0x5e0
swapin_readahead+0x92/0x8dc
do_swap_page+0x49b/0xf20
__handle_mm_fault+0xcfb/0xd70
handle_mm_fault+0xfc/0x2f0
do_page_fault+0x263/0x715
page_fault+0x34/0x40
1 lock held by systemd/1:
#0: ffff897c38f14858 (&mm->mmap_sem#2){++++}-{3:3}, at: do_page_fault+0x143/0x715
irq event stamp: 43530289
count_memcg_event_mm+0x1a6/0x270
count_memcg_event_mm+0x119/0x270
__do_softirq+0x365/0x589
irq_exit+0xa2/0xc0
Signed-off-by: Qian Cai <cai@xxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Marco Elver <elver@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/20200402213748.2237-1-cai@xxxxxx
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/mm/swap_state.c b/mm/swap_state.c
index 4ce014dc4571a..7c434fcfff0dd 100644
--- a/mm/swap_state.c
+++ b/mm/swap_state.c
@@ -511,10 +511,11 @@ static unsigned long swapin_nr_pages(unsigned long offset)
return 1;
hits = atomic_xchg(&swapin_readahead_hits, 0);
- pages = __swapin_nr_pages(prev_offset, offset, hits, max_pages,
+ pages = __swapin_nr_pages(READ_ONCE(prev_offset), offset, hits,
+ max_pages,
atomic_read(&last_readahead_pages));
if (!hits)
- prev_offset = offset;
+ WRITE_ONCE(prev_offset, offset);
atomic_set(&last_readahead_pages, pages);
return pages;
