mbcache: don't reclaim used entries

mbcache: don't reclaim used entries

[ Upstream commit 09131fcd92ff1fe3dc5ab78267fc4d7cf754fae9 ]

Do not reclaim entries that are currently used by somebody from a
shrinker. Firstly, these entries are likely useful. Secondly, we will
need to keep such entries to protect pending increment of xattr block
refcount.

CC: stable@vger.kernel.org
Fixes: 75980e9575cf ("ext4: convert to mbcache2")
Signed-off-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/20220712105436.32204-1-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Stable-dep-of: 246b6193fbe5 ("ext4: fix deadlock due to mbcache entry corruption")
Signed-off-by: Sasha Levin <sashal@kernel.org>