6.1-stable review patch. If anyone has any objections, please let me know. ------------------ From: linke li <lilinke99@xxxxxx> [ 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> --- lib/sbitmap.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/lib/sbitmap.c b/lib/sbitmap.c index b942f2ba9a415..a727d0b12763a 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)) ; -- 2.43.0
