From d01730d74d2b0155da50d44555001706294014f7 Mon Sep 17 00:00:00 2001 From: Jiaying Zhang Date: Tue, 7 Jul 2009 18:15:21 +0200 Subject: [PATCH] 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 Signed-off-by: Jan Kara --- fs/quota/dquot.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c index 607c579e5ec..70f36c043d6 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); -- 2.20.1