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From:   wuchi <wuchi.zero@gmail.com>
To:     axboe@kernel.dk, mwilck@suse.com, andriy.shevchenko@linux.intel.com
Cc:     linux-block@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH] lib/sbitmap: Fix invalid loop in __sbitmap_queue_get_batch()
Date:   Sun,  5 Jun 2022 22:58:35 +0800
Message-Id: <20220605145835.26916-1-wuchi.zero@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

1. Getting next index before continue branch.
2. Checking free bits when setting the target bits. Otherwise,
it may reuse the busying bits.

Signed-off-by: wuchi <wuchi.zero@gmail.com>
---
 lib/sbitmap.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/lib/sbitmap.c b/lib/sbitmap.c
index ae4fd4de9ebe..29eb0484215a 100644
--- a/lib/sbitmap.c
+++ b/lib/sbitmap.c
@@ -528,7 +528,7 @@ unsigned long __sbitmap_queue_get_batch(struct sbitmap_queue *sbq, int nr_tags,
 
 		sbitmap_deferred_clear(map);
 		if (map->word == (1UL << (map_depth - 1)) - 1)
-			continue;
+			goto next;
 
 		nr = find_first_zero_bit(&map->word, map_depth);
 		if (nr + nr_tags <= map_depth) {
@@ -539,6 +539,8 @@ unsigned long __sbitmap_queue_get_batch(struct sbitmap_queue *sbq, int nr_tags,
 			get_mask = ((1UL << map_tags) - 1) << nr;
 			do {
 				val = READ_ONCE(map->word);
+				if ((val & ~get_mask) != val)
+					goto next;
 				ret = atomic_long_cmpxchg(ptr, val, get_mask | val);
 			} while (ret != val);
 			get_mask = (get_mask & ~ret) >> nr;
@@ -549,6 +551,7 @@ unsigned long __sbitmap_queue_get_batch(struct sbitmap_queue *sbq, int nr_tags,
 				return get_mask;
 			}
 		}
+next:
 		/* Jump to next index. */
 		if (++index >= sb->map_nr)
 			index = 0;
-- 
2.20.1