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authorJiaying Zhang <jiayingz@google.com>2009-07-07 18:15:21 +0200
committerJan Kara <jack@suse.cz>2009-07-07 18:15:21 +0200
commitd01730d74d2b0155da50d44555001706294014f7 (patch)
treea6de6075c054b6f253be19062d7f8efc973d55dc
parentfaf80d62e44dc627efb741f48db50c1858d1667c (diff)
downloadop-kernel-dev-d01730d74d2b0155da50d44555001706294014f7.zip
op-kernel-dev-d01730d74d2b0155da50d44555001706294014f7.tar.gz
quota: Fix possible deadlock during parallel quotaon and quotaoff
The following test script triggers a deadlock on ext2 filesystem: while true; do quotaon /dev/hda >&/dev/null; usleep $RANDOM; done & while true; do quotaoff /dev/hda >&/dev/null; usleep $RANDOM; done & I found there is a potential deadlock between quotaon and quotaoff (or quotasync). Basically, all of quotactl operations need to be protected by dqonoff_mutex. vfs_quota_off and vfs_quota_sync also call sb->s_op->quota_write that needs to grab the i_mutex of the quota file. But in vfs_quota_on_inode (called from quotaon operation), the current code tries to grab the i_mutex of the quota file first before getting quonoff_mutex. Reverse the order in which we take locks in vfs_quota_on_inode(). Jan Kara: Changed changelog to be more readable, made lockdep happy with I_MUTEX_QUOTA. Signed-off-by: Jiaying Zhang <jiayingz@google.com> Signed-off-by: Jan Kara <jack@suse.cz>
-rw-r--r--fs/quota/dquot.c4
1 files changed, 2 insertions, 2 deletions
diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index 607c579..70f36c0 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -2042,8 +2042,8 @@ static int vfs_load_quota_inode(struct inode *inode, int type, int format_id,
* changes */
invalidate_bdev(sb->s_bdev);
}
- mutex_lock(&inode->i_mutex);
mutex_lock(&dqopt->dqonoff_mutex);
+ mutex_lock_nested(&inode->i_mutex, I_MUTEX_QUOTA);
if (sb_has_quota_loaded(sb, type)) {
error = -EBUSY;
goto out_lock;
@@ -2094,7 +2094,6 @@ out_file_init:
dqopt->files[type] = NULL;
iput(inode);
out_lock:
- mutex_unlock(&dqopt->dqonoff_mutex);
if (oldflags != -1) {
down_write(&dqopt->dqptr_sem);
/* Set the flags back (in the case of accidental quotaon()
@@ -2104,6 +2103,7 @@ out_lock:
up_write(&dqopt->dqptr_sem);
}
mutex_unlock(&inode->i_mutex);
+ mutex_unlock(&dqopt->dqonoff_mutex);
out_fmt:
put_quota_format(fmt);
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