From: Kemeng Shi Date: Mon, 16 Jan 2023 20:50:56 +0000 (+0800) Subject: sbitmap: remove redundant check in __sbitmap_queue_get_batch X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=903e86f3a64d9573352bbab2f211fdbbaa5772b7;p=linux.git sbitmap: remove redundant check in __sbitmap_queue_get_batch Commit fbb564a557809 ("lib/sbitmap: Fix invalid loop in __sbitmap_queue_get_batch()") mentioned that "Checking free bits when setting the target bits. Otherwise, it may reuse the busying bits." This commit add check to make sure all masked bits in word before cmpxchg is zero. Then the existing check after cmpxchg to check any zero bit is existing in masked bits in word is redundant. Actually, old value of word before cmpxchg is stored in val and we will filter out busy bits in val by "(get_mask & ~val)" after cmpxchg. So we will not reuse busy bits methioned in commit fbb564a557809 ("lib/sbitmap: Fix invalid loop in __sbitmap_queue_get_batch()"). Revert new-added check to remove redundant check. Fixes: fbb564a55780 ("lib/sbitmap: Fix invalid loop in __sbitmap_queue_get_batch()") Reviewed-by: Jan Kara Signed-off-by: Kemeng Shi Link: https://lore.kernel.org/r/20230116205059.3821738-3-shikemeng@huaweicloud.com Signed-off-by: Jens Axboe --- diff --git a/lib/sbitmap.c b/lib/sbitmap.c index 462873a4337c8..eb45a2d7916e2 100644 --- a/lib/sbitmap.c +++ b/lib/sbitmap.c @@ -518,11 +518,9 @@ unsigned long __sbitmap_queue_get_batch(struct sbitmap_queue *sbq, int nr_tags, get_mask = ((1UL << nr_tags) - 1) << nr; val = READ_ONCE(map->word); - do { - if ((val & ~get_mask) != val) - goto next; - } while (!atomic_long_try_cmpxchg(ptr, &val, - get_mask | val)); + while (!atomic_long_try_cmpxchg(ptr, &val, + get_mask | val)) + ; get_mask = (get_mask & ~val) >> nr; if (get_mask) { *offset = nr + (index << sb->shift);