diff options
| author | linke li <lilinke99@qq.com> | 2024-04-26 18:34:44 +0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2024-08-03 08:49:29 +0200 |
| commit | aba6f11e23f89e63ae7f2ceb22ffc35b8f359cc6 (patch) | |
| tree | c16e2b73d2c736c2b68b460b2c1046eed5062813 | |
| parent | 0de2fb1f78e98e4654c9e4544118dd1d1cf5bc48 (diff) | |
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@qq.com>
Link: https://lore.kernel.org/r/tencent_0B517C25E519D3D002194E8445E86C04AD0A@qq.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Stable-dep-of: 72d04bdcf3f7 ("sbitmap: fix io hung due to race on sbitmap_word::cleared")
Signed-off-by: Sasha Levin <sashal@kernel.org>
| -rw-r--r-- | lib/sbitmap.c | 8 |
1 files changed, 4 insertions, 4 deletions
diff --git a/lib/sbitmap.c b/lib/sbitmap.c index b942f2ba9a41..a727d0b12763 100644 --- a/lib/sbitmap.c +++ b/lib/sbitmap.c @@ -503,18 +503,18 @@ 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)) ; |