This is a note to let you know that I've just added the patch titled
sbitmap: use READ_ONCE to access map->word
to the 6.6-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:
sbitmap-use-read_once-to-access-map-word.patch
and it can be found in the queue-6.6 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 27fe5b47611cacb0fb53db941ec41ebbc8e31c1e
Author: linke li <lilinke99@xxxxxx>
Date: Fri Apr 26 18:34:44 2024 +0800
sbitmap: use READ_ONCE to access map->word
[ Upstream commit 6ad0d7e0f4b68f87a98ea2b239123b7d865df86b ]
In __sbitmap_queue_get_batch(), map->word is read several times, and
update atomically using atomic_long_try_cmpxchg(). But the first two read
of map->word is not protected.
This patch moves the statement val = READ_ONCE(map->word) forward,
eliminating unprotected accesses to map->word within the function.
It is aimed at reducing the number of benign races reported by KCSAN in
order to focus future debugging effort on harmful races.
Signed-off-by: linke li <lilinke99@xxxxxx>
Link: https://lore.kernel.org/r/tencent_0B517C25E519D3D002194E8445E86C04AD0A@xxxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Stable-dep-of: 72d04bdcf3f7 ("sbitmap: fix io hung due to race on sbitmap_word::cleared")
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index d0a5081dfd122..d1247f34d584e 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -499,18 +499,18 @@ unsigned long __sbitmap_queue_get_batch(struct sbitmap_queue *sbq, int nr_tags,
struct sbitmap_word *map = &sb->map[index];
unsigned long get_mask;
unsigned int map_depth = __map_depth(sb, index);
+ unsigned long val;
sbitmap_deferred_clear(map);
- if (map->word == (1UL << (map_depth - 1)) - 1)
+ val = READ_ONCE(map->word);
+ if (val == (1UL << (map_depth - 1)) - 1)
goto next;
- nr = find_first_zero_bit(&map->word, map_depth);
+ nr = find_first_zero_bit(&val, map_depth);
if (nr + nr_tags <= map_depth) {
atomic_long_t *ptr = (atomic_long_t *) &map->word;
- unsigned long val;
get_mask = ((1UL << nr_tags) - 1) << nr;
- val = READ_ONCE(map->word);
while (!atomic_long_try_cmpxchg(ptr, &val,
get_mask | val))
;
