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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>
This commit is contained in:
Jan Kara 2012-04-25 21:15:53 +02:00
parent f9ef178412
commit a80b12c3d0
1 changed files with 6 additions and 8 deletions
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14
fs/quota/dquot.c
View File

@ -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 @@ static int vfs_load_quota_inode(struct inode *inode, int type, int format_id,
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);