shmem: put_super must percpu_counter_destroy

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-bisected-and-tested-by: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/shmem.c

@@ -2325,7 +2325,10 @@ static int shmem_show_options(struct seq_file *seq, struct vfsmount *vfs)
 
 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 *sb, void *data, int silent)
 #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;