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Commit 26245c94 authored by Jan Kara's avatar Jan Kara
Browse files

quota: Cleanup S_NOQUOTA handling 



Cleanup handling of S_NOQUOTA inode flag and document it a bit. The flag
does not have to be set under dqptr_sem. Only functions modifying inode's
dquot pointers have to check the flag under dqptr_sem before going forward
with the modification. This way we are sure that we cannot add new dquot
pointers to the inode which is just becoming a quota file.

The good thing about this cleanup is that there are no more places in quota
code which enforce i_mutex vs. dqptr_sem lock ordering (in particular that
dqptr_sem -> i_mutex of quota file). This should silence some (false) lockdep
warnings with ext4 + quota and generally make life of some filesystems easier.

Signed-off-by: default avatarJan Kara <jack@suse.cz>
parent 3a5b27bf

fs/quota/dquot.c

+11 −36
Original line number Diff line number Diff line
@@ -100,9 +100,13 @@ 
 *

 * Any operation working on dquots via inode pointers must hold dqptr_sem.  If

 * operation is just reading pointers from inode (or not using them at all) the

 * read lock is enough. If pointers are altered function must hold write lock

 * (these locking rules also apply for S_NOQUOTA flag in the inode - note that

 * for altering the flag i_mutex is also needed).

 * read lock is enough. If pointers are altered function must hold write lock.

 * Special care needs to be taken about S_NOQUOTA inode flag (marking that

 * inode is a quota file). Functions adding pointers from inode to dquots have

 * to check this flag under dqptr_sem and then (if S_NOQUOTA is not set) they

 * have to do all pointer modifications before dropping dqptr_sem. This makes

 * sure they cannot race with quotaon which first sets S_NOQUOTA flag and

 * then drops all pointers to dquots from an inode.

 *

 * Each dquot has its dq_lock mutex. Locked dquots might not be referenced

 * from inodes (dquot_alloc_space() and such don't check the dq_lock).
@@ -1275,7 +1279,6 @@ int dquot_initialize(struct inode *inode, int type) 
	}



	down_write(&sb_dqopt(sb)->dqptr_sem);

	/* Having dqptr_sem we know NOQUOTA flags can't be altered... */

	if (IS_NOQUOTA(inode))

		goto out_err;

	for (cnt = 0; cnt < MAXQUOTAS; cnt++) {
@@ -1431,11 +1434,6 @@ int __dquot_alloc_space(struct inode *inode, qsize_t number, 
	}



	down_read(&sb_dqopt(inode->i_sb)->dqptr_sem);

	if (IS_NOQUOTA(inode)) {

		inode_incr_space(inode, number, reserve);

		goto out_unlock;

	}



	for (cnt = 0; cnt < MAXQUOTAS; cnt++)

		warntype[cnt] = QUOTA_NL_NOWARN;
@@ -1466,7 +1464,6 @@ int __dquot_alloc_space(struct inode *inode, qsize_t number, 
	mark_all_dquot_dirty(inode->i_dquot);

out_flush_warn:

	flush_warnings(inode->i_dquot, warntype);

out_unlock:

	up_read(&sb_dqopt(inode->i_sb)->dqptr_sem);

out:

	return ret;
@@ -1499,10 +1496,6 @@ int dquot_alloc_inode(const struct inode *inode, qsize_t number) 
	for (cnt = 0; cnt < MAXQUOTAS; cnt++)

		warntype[cnt] = QUOTA_NL_NOWARN;

	down_read(&sb_dqopt(inode->i_sb)->dqptr_sem);

	if (IS_NOQUOTA(inode)) {

		up_read(&sb_dqopt(inode->i_sb)->dqptr_sem);

		return QUOTA_OK;

	}

	spin_lock(&dq_data_lock);

	for (cnt = 0; cnt < MAXQUOTAS; cnt++) {

		if (!inode->i_dquot[cnt])
@@ -1539,12 +1532,6 @@ int dquot_claim_space(struct inode *inode, qsize_t number) 
	}



	down_read(&sb_dqopt(inode->i_sb)->dqptr_sem);

	if (IS_NOQUOTA(inode))	{

		up_read(&sb_dqopt(inode->i_sb)->dqptr_sem);

		inode_claim_rsv_space(inode, number);

		goto out;

	}



	spin_lock(&dq_data_lock);

	/* Claim reserved quotas to allocated quotas */

	for (cnt = 0; cnt < MAXQUOTAS; cnt++) {
@@ -1573,17 +1560,11 @@ int __dquot_free_space(struct inode *inode, qsize_t number, int reserve) 
	/* First test before acquiring mutex - solves deadlocks when we

         * re-enter the quota code and are already holding the mutex */

	if (IS_NOQUOTA(inode)) {

out_sub:

		inode_decr_space(inode, number, reserve);

		return QUOTA_OK;

	}



	down_read(&sb_dqopt(inode->i_sb)->dqptr_sem);

	/* Now recheck reliably when holding dqptr_sem */

	if (IS_NOQUOTA(inode)) {

		up_read(&sb_dqopt(inode->i_sb)->dqptr_sem);

		goto out_sub;

	}

	spin_lock(&dq_data_lock);

	for (cnt = 0; cnt < MAXQUOTAS; cnt++) {

		if (!inode->i_dquot[cnt])
@@ -1636,11 +1617,6 @@ int dquot_free_inode(const struct inode *inode, qsize_t number) 
		return QUOTA_OK;



	down_read(&sb_dqopt(inode->i_sb)->dqptr_sem);

	/* Now recheck reliably when holding dqptr_sem */

	if (IS_NOQUOTA(inode)) {

		up_read(&sb_dqopt(inode->i_sb)->dqptr_sem);

		return QUOTA_OK;

	}

	spin_lock(&dq_data_lock);

	for (cnt = 0; cnt < MAXQUOTAS; cnt++) {

		if (!inode->i_dquot[cnt])
@@ -1692,7 +1668,6 @@ int dquot_transfer(struct inode *inode, struct iattr *iattr) 
					      GRPQUOTA);



	down_write(&sb_dqopt(inode->i_sb)->dqptr_sem);

	/* Now recheck reliably when holding dqptr_sem */

	if (IS_NOQUOTA(inode)) {	/* File without quota accounting? */

		up_write(&sb_dqopt(inode->i_sb)->dqptr_sem);

		goto put_all;
@@ -2010,13 +1985,15 @@ 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. */

		down_write(&dqopt->dqptr_sem);

		mutex_lock_nested(&inode->i_mutex, I_MUTEX_QUOTA);

		oldflags = inode->i_flags & (S_NOATIME | S_IMMUTABLE |

					     S_NOQUOTA);

		inode->i_flags |= S_NOQUOTA | S_NOATIME | S_IMMUTABLE;

		mutex_unlock(&inode->i_mutex);

		up_write(&dqopt->dqptr_sem);

		/*

		 * When S_NOQUOTA is set, remove dquot references as no more

		 * references can be added

		 */

		sb->dq_op->drop(inode);

	}
@@ -2053,14 +2030,12 @@ static int vfs_load_quota_inode(struct inode *inode, int type, int format_id, 
	iput(inode);

out_lock:

	if (oldflags != -1) {

		down_write(&dqopt->dqptr_sem);

		mutex_lock_nested(&inode->i_mutex, I_MUTEX_QUOTA);

		/* 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);

		inode->i_flags |= oldflags;

		mutex_unlock(&inode->i_mutex);

		up_write(&dqopt->dqptr_sem);

	}

	mutex_unlock(&dqopt->dqonoff_mutex);

out_fmt: