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: Jan Kara <jack@suse.cz>
diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index 3fc62b0..f6eaf0d 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -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 @@
}
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 @@
}
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 @@
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 @@
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 @@
}
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 @@
/* 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 @@
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 @@
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 @@
/* 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 @@
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: