[PATCH] shmem: fix percpu_counters list corruption

[Hugh Dickins <hughd@google.com>]

list_add() corruption messages reported from shmem_fill_super()'s recently
introduced percpu_counter_init(): shmem_put_super() needs to remember to
percpu_counter_destroy().  And also check error from percpu_counter_init().

Reported to fix oopses in __free_pipe_info() but I cannot work that out!

Reported-and-bisected-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: Hugh Dickins <hughd@google.com>
Tested-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
---

 mm/shmem.c |    8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

--- 2.6.36-rc1/mm/shmem.c	2010-08-16 00:18:01.000000000 -0700
+++ linux/mm/shmem.c	2010-08-17 14:42:56.000000000 -0700
@@ -2325,7 +2325,10 @@ static int shmem_show_options(struct seq
 
 static void shmem_put_super(struct super_block *sb)
 {
-	kfree(sb->s_fs_info);
+	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
+
+	percpu_counter_destroy(&sbinfo->used_blocks);
+	kfree(sbinfo);
 	sb->s_fs_info = NULL;
 }
 
@@ -2367,7 +2370,8 @@ int shmem_fill_super(struct super_block
 #endif
 
 	spin_lock_init(&sbinfo->stat_lock);
-	percpu_counter_init(&sbinfo->used_blocks, 0);
+	if (percpu_counter_init(&sbinfo->used_blocks, 0))
+		goto failed;
 	sbinfo->free_inodes = sbinfo->max_inodes;
 
 	sb->s_maxbytes = SHMEM_MAX_BYTES;