quota: Get rid of nested I_MUTEX_QUOTA locking subclass

So far i_mutex was ranking above dqonoff_mutex and i_mutex on quota files
was special and ranking below dqonoff_mutex (and several other locks).
However there's no real need for i_mutex on quota files to be special.
IO on quota files is serialized by dqio_mutex anyway so we don't need to
take i_mutex when writing to quota files. Other places where we take i_mutex
on quota file can accomodate standard i_mutex lock ranking, we only need
to change the lock ranking to be dqonoff_mutex > i_mutex which is a matter
of changing documentation because there's no place which would enforce
ordering in the other direction.

Signed-off-by: Jan Kara <jack@suse.cz>

diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index 6e429fd..10cbe84 100644 (file)
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -116,15 +116,15 @@
  * spinlock to internal buffers before writing.
  *
  * Lock ordering (including related VFS locks) is the following:
- *   i_mutex > dqonoff_sem > journal_lock > dqptr_sem > dquot->dq_lock >
+ *   dqonoff_mutex > i_mutex > journal_lock > dqptr_sem > dquot->dq_lock >
  *   dqio_mutex
+ * dqonoff_mutex > i_mutex comes from dquot_quota_sync, dquot_enable, etc.
  * The lock ordering of dqptr_sem imposed by quota code is only dqonoff_sem >
  * dqptr_sem. But filesystem has to count with the fact that functions such as
  * dquot_alloc_space() acquire dqptr_sem and they usually have to be called
  * from inside a transaction to keep filesystem consistency after a crash. Also
  * filesystems usually want to do some IO on dquot from ->mark_dirty which is
  * called with dqptr_sem held.
- * i_mutex on quota files is special (it's below dqio_mutex)
  */
 
 static __cacheline_aligned_in_smp DEFINE_SPINLOCK(dq_list_lock);
@@ -658,8 +658,7 @@ int dquot_quota_sync(struct super_block *sb, int type, int wait)
                        continue;
                if (!sb_has_quota_active(sb, cnt))
                        continue;
-               mutex_lock_nested(&dqopt->files[cnt]->i_mutex,
-                                 I_MUTEX_QUOTA);
+               mutex_lock(&dqopt->files[cnt]->i_mutex);
                truncate_inode_pages(&dqopt->files[cnt]->i_data, 0);
                mutex_unlock(&dqopt->files[cnt]->i_mutex);
        }
@@ -2037,8 +2036,7 @@ int dquot_disable(struct super_block *sb, int type, unsigned int flags)
                        /* If quota was reenabled in the meantime, we have
                         * nothing to do */
                        if (!sb_has_quota_loaded(sb, cnt)) {
-                               mutex_lock_nested(&toputinode[cnt]->i_mutex,
-                                                 I_MUTEX_QUOTA);
+                               mutex_lock(&toputinode[cnt]->i_mutex);
                                toputinode[cnt]->i_flags &= ~(S_IMMUTABLE |
                                  S_NOATIME | S_NOQUOTA);
                                truncate_inode_pages(&toputinode[cnt]->i_data,
@@ -2133,7 +2131,7 @@ static int vfs_load_quota_inode(struct inode *inode, int type, int format_id,
                /* We don't want quota and atime on quota files (deadlocks
                 * possible) Also nobody should write to the file - we use
                 * special IO operations which ignore the immutable bit. */
-               mutex_lock_nested(&inode->i_mutex, I_MUTEX_QUOTA);
+               mutex_lock(&inode->i_mutex);
                oldflags = inode->i_flags & (S_NOATIME | S_IMMUTABLE |
                                             S_NOQUOTA);
                inode->i_flags |= S_NOQUOTA | S_NOATIME | S_IMMUTABLE;
@@ -2180,7 +2178,7 @@ out_file_init:
        iput(inode);
 out_lock:
        if (oldflags != -1) {
-               mutex_lock_nested(&inode->i_mutex, I_MUTEX_QUOTA);
+               mutex_lock(&inode->i_mutex);
                /* Set the flags back (in the case of accidental quotaon()
                 * on a wrong file we don't want to mess up the flags) */
                inode->i_flags &= ~(S_NOATIME | S_NOQUOTA | S_IMMUTABLE);