UBIFS: fix shrinker object count reports

commit cf610bf4199770420629d3bc273494bd27ad6c1d upstream.

Sometimes VM asks the shrinker to return amount of objects it can shrink,
and we return the ubifs_clean_zn_cnt in that case. However, it is possible
that this counter is negative for a short period of time, due to the way
UBIFS TNC code updates it. And I can observe the following warnings sometimes:

shrink_slab: ubifs_shrinker+0x0/0x2b7 [ubifs] negative objects to delete nr=-8541616642706119788

This patch makes sure UBIFS never returns negative count of objects.

Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Andi Kleen <ak@linux.intel.com>

diff --git a/fs/ubifs/shrinker.c b/fs/ubifs/shrinker.c
index 0b201114a5adf9cfc9c04b6730442748c079fa9d..5306c9195ed8ce813ded41997c7dbe0e374688d6 100644 (file)
--- a/fs/ubifs/shrinker.c
+++ b/fs/ubifs/shrinker.c
@@ -283,7 +283,11 @@ int ubifs_shrinker(struct shrinker *shrink, int nr, gfp_t gfp_mask)
        long clean_zn_cnt = atomic_long_read(&ubifs_clean_zn_cnt);
 
        if (nr == 0)
-               return clean_zn_cnt;
+               /*
+                * Due to the way UBIFS updates the clean znode counter it may
+                * temporarily be negative.
+                */
+               return clean_zn_cnt >= 0 ? clean_zn_cnt : 1;
 
        if (!clean_zn_cnt) {
                /*