linux-kernel - [PATCH 3.16 079/202] fs/dcache: Fix incorrect nr_dentry_unused accounting in shrink_dcache

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Message-ID: <lsq.1556377989.189435994@decadent.org.uk>
Date:   Sat, 27 Apr 2019 16:13:09 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Waiman Long" <longman@...hat.com>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>,
        "Dave Chinner" <dchinner@...hat.com>
Subject: [PATCH 3.16 079/202] fs/dcache: Fix incorrect nr_dentry_unused
 accounting in shrink_dcache_sb()

3.16.66-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Waiman Long <longman@...hat.com>

commit 1dbd449c9943e3145148cc893c2461b72ba6fef0 upstream.

The nr_dentry_unused per-cpu counter tracks dentries in both the LRU
lists and the shrink lists where the DCACHE_LRU_LIST bit is set.

The shrink_dcache_sb() function moves dentries from the LRU list to a
shrink list and subtracts the dentry count from nr_dentry_unused.  This
is incorrect as the nr_dentry_unused count will also be decremented in
shrink_dentry_list() via d_shrink_del().

To fix this double decrement, the decrement in the shrink_dcache_sb()
function is taken out.

Fixes: 4e717f5c1083 ("list_lru: remove special case function list_lru_dispose_all."
Signed-off-by: Waiman Long <longman@...hat.com>
Reviewed-by: Dave Chinner <dchinner@...hat.com>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 fs/dcache.c | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -1063,15 +1063,11 @@ static enum lru_status dentry_lru_isolat
  */
 void shrink_dcache_sb(struct super_block *sb)
 {
-	long freed;
-
 	do {
 		LIST_HEAD(dispose);
 
-		freed = list_lru_walk(&sb->s_dentry_lru,
+		list_lru_walk(&sb->s_dentry_lru,
 			dentry_lru_isolate_shrink, &dispose, 1024);
-
-		this_cpu_sub(nr_dentry_unused, freed);
 		shrink_dentry_list(&dispose);
 		cond_resched();
 	} while (list_lru_count(&sb->s_dentry_lru) > 0);