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Commit a80b12c3 authored by Jan Kara's avatar Jan Kara
Browse files

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: default avatarJan Kara <jack@suse.cz>
parent f9ef1784

fs/quota/dquot.c

+6 −8
Original line number Diff line number Diff line
@@ -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);