dm cache: optimize dirty bit checking with find_next_bit when resizing
stable inclusion
from stable-v5.10.230
commit f136d8d3f26fd5113e80ba7c70f7e9a5932295b3
category: bugfix
bugzilla: https://gitee.com/src-openeuler/kernel/issues/IB5AV2
CVE: CVE-2024-50278
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f136d8d3f26fd5113e80ba7c70f7e9a5932295b3
--------------------------------
commit f484697e619a83ecc370443a34746379ad99d204 upstream.
When shrinking the fast device, dm-cache iteratively searches for a
dirty bit among the cache blocks to be dropped, which is less efficient.
Use find_next_bit instead, as it is twice as fast as the iterative
approach with test_bit.
Signed-off-by: Ming-Hung Tsai <mtsai@redhat.com>
Fixes: f494a9c6b1b6 ("dm cache: cache shrinking support")
Cc: stable@vger.kernel.org
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Acked-by: Joe Thornber <thornber@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Zheng Qixing <zhengqixing@huawei.com>
diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index 263c0eb..8ccf442 100644
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -2960,14 +2960,14 @@ static bool can_resize(struct cache *cache, dm_cblock_t new_size)
/*
* We can't drop a dirty block when shrinking the cache.
*/
- while (from_cblock(new_size) < from_cblock(cache->cache_size)) {
- if (is_dirty(cache, new_size)) {
- DMERR("%s: unable to shrink cache; cache block %llu is dirty",
- cache_device_name(cache),
- (unsigned long long) from_cblock(new_size));
- return false;
- }
- new_size = to_cblock(from_cblock(new_size) + 1);
+ new_size = to_cblock(find_next_bit(cache->dirty_bitset,
+ from_cblock(cache->cache_size),
+ from_cblock(new_size)));
+ if (new_size != cache->cache_size) {
+ DMERR("%s: unable to shrink cache; cache block %llu is dirty",
+ cache_device_name(cache),
+ (unsigned long long) from_cblock(new_size));
+ return false;
}
return true;
