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Subject[53/53] vmscan: fix shrinker callback bug in fs/super.c
3.1-stable review patch.  If anyone has any objections, please let me know.

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

From: Mikulas Patocka <mpatocka@redhat.com>

commit 09f363c7363eb10cfb4b82094bd7064e5608258b upstream.

The callback must not return -1 when nr_to_scan is zero. Fix the bug in
fs/super.c and add this requirement to the callback specification.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: Dave Chinner <david@fromorbit.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
fs/super.c | 2 +-
include/linux/shrinker.h | 1 +
2 files changed, 2 insertions(+), 1 deletion(-)

--- a/fs/super.c
+++ b/fs/super.c
@@ -61,7 +61,7 @@ static int prune_super(struct shrinker *
return -1;

if (!grab_super_passive(sb))
- return -1;
+ return !sc->nr_to_scan ? 0 : -1;

if (sb->s_op && sb->s_op->nr_cached_objects)
fs_objects = sb->s_op->nr_cached_objects(sb);
--- a/include/linux/shrinker.h
+++ b/include/linux/shrinker.h
@@ -20,6 +20,7 @@ struct shrink_control {
* 'nr_to_scan' entries and attempt to free them up. It should return
* the number of objects which remain in the cache. If it returns -1, it means
* it cannot do any scanning at this time (eg. there is a risk of deadlock).
+ * The callback must not return -1 if nr_to_scan is zero.
*
* The 'gfpmask' refers to the allocation we are currently trying to
* fulfil.



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