This is a note to let you know that I've just added the patch titled
sbitmap: remove redundant check in __sbitmap_queue_get_batch
to the 6.1-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-remove-redundant-check-in-__sbitmap_queue_ge.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 9f618264c3c5cc86d8c5fe38cfd9a6b6842a8560
Author: Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx>
Date: Tue Jan 17 04:50:56 2023 +0800
sbitmap: remove redundant check in __sbitmap_queue_get_batch
[ Upstream commit 903e86f3a64d9573352bbab2f211fdbbaa5772b7 ]
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 <jack@xxxxxxx>
Signed-off-by: Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/20230116205059.3821738-3-shikemeng@xxxxxxxxxxxxxxx
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index 7280ae8ca88c7..ca099fbc6f3c9 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -537,11 +537,9 @@ 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);
