circular locking dependency found in QUOTA OFF

i_mutex on quota files is special.  Unlike i_mutexes for other inodes it is
acquired under dqonoff_mutex.  Tell lockdep about this lock ranking.  Also
comment and code in quota_sync_sb() seem to be bogus (as i_mutex for quota
file can be acquired under dqonoff_mutex).  Move truncate_inode_pages()
call under dqonoff_mutex and save some problems with races...

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 16 deletions

diff --git a/fs/quota.c b/fs/quota.c
index e9d88fd0eca8..9f237d6182c9 100644
--- a/fs/quota.c
+++ b/fs/quota.c
@@ -157,7 +157,6 @@ static int check_quotactl_valid(struct super_block *sb, int type, int cmd, qid_t
 static void quota_sync_sb(struct super_block *sb, int type)
 {
         int cnt;
-        struct inode *discard[MAXQUOTAS];
 
         sb->s_qcop->quota_sync(sb, type);
         /* This is not very clever (and fast) but currently I don't know about
@@ -167,29 +166,21 @@ static void quota_sync_sb(struct super_block *sb, int type)
                 sb->s_op->sync_fs(sb, 1);
         sync_blockdev(sb->s_bdev);
 
-        /* Now when everything is written we can discard the pagecache so
-         * that userspace sees the changes. We need i_mutex and so we could
-         * not do it inside dqonoff_mutex. Moreover we need to be carefull
-         * about races with quotaoff() (that is the reason why we have own
-         * reference to inode). */
+        /*
+         * Now when everything is written we can discard the pagecache so
+         * that userspace sees the changes.
+         */
         mutex_lock(&sb_dqopt(sb)->dqonoff_mutex);
         for (cnt = 0; cnt < MAXQUOTAS; cnt++) {
-                discard[cnt] = NULL;
                 if (type != -1 && cnt != type)
                         continue;
                 if (!sb_has_quota_enabled(sb, cnt))
                         continue;
-                discard[cnt] = igrab(sb_dqopt(sb)->files[cnt]);
+                mutex_lock_nested(&sb_dqopt(sb)->files[cnt]->i_mutex, I_MUTEX_QUOTA);
+                truncate_inode_pages(&sb_dqopt(sb)->files[cnt]->i_data, 0);
+                mutex_unlock(&sb_dqopt(sb)->files[cnt]->i_mutex);
         }
         mutex_unlock(&sb_dqopt(sb)->dqonoff_mutex);
-        for (cnt = 0; cnt < MAXQUOTAS; cnt++) {
-                if (discard[cnt]) {
-                        mutex_lock(&discard[cnt]->i_mutex);
-                        truncate_inode_pages(&discard[cnt]->i_data, 0);
-                        mutex_unlock(&discard[cnt]->i_mutex);
-                        iput(discard[cnt]);
-                }
-        }
 }
 
 void sync_dquots(struct super_block *sb, int type)