[3.13.y.z extended stable] Patch "fs: Fix theoretical division by 0 in super_cache_scan()." has been added to staging queue

Kamal Mostafa kamal at canonical.com
Tue Oct 21 20:09:30 UTC 2014

This is a note to let you know that I have just added a patch titled

    fs: Fix theoretical division by 0 in super_cache_scan().

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:


This patch is scheduled to be released in version

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.13.y.z tree, see



>From b92a2fc33619cf3aadd46ed4ac66e3b53b4f2cc2 Mon Sep 17 00:00:00 2001
From: Tetsuo Handa <penguin-kernel at I-love.SAKURA.ne.jp>
Date: Sat, 17 May 2014 20:56:38 +0900
Subject: fs: Fix theoretical division by 0 in super_cache_scan().

commit 475d0db742e3755c6b267f48577ff7cbb7dfda0d upstream.

total_objects could be 0 and is used as a denom.

While total_objects is a "long", total_objects == 0 unlikely happens for
3.12 and later kernels because 32-bit architectures would not be able to
hold (1 << 32) objects. However, total_objects == 0 may happen for kernels
between 3.1 and 3.11 because total_objects in prune_super() was an "int"
and (e.g.) x86_64 architecture might be able to hold (1 << 32) objects.

Signed-off-by: Tetsuo Handa <penguin-kernel at I-love.SAKURA.ne.jp>
Reviewed-by: Christoph Hellwig <hch at lst.de>
Signed-off-by: Al Viro <viro at zeniv.linux.org.uk>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
 fs/super.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/fs/super.c b/fs/super.c
index e5f6c2c..97edaa93 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -81,6 +81,8 @@ static unsigned long super_cache_scan(struct shrinker *shrink,
 	inodes = list_lru_count_node(&sb->s_inode_lru, sc->nid);
 	dentries = list_lru_count_node(&sb->s_dentry_lru, sc->nid);
 	total_objects = dentries + inodes + fs_objects + 1;
+	if (!total_objects)
+		total_objects = 1;

 	/* proportion the scan between the caches */
 	dentries = mult_frac(sc->nr_to_scan, dentries, total_objects);

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