quota: Fix WARN_ON in lookup_one_len

We should hold i_mutex when looking up quota files for journaled quotas,
otherwise a WARN_ON in lookup_one_len triggers. The fact that we didn't
hold i_mutex previously probably could not lead to a real bug since the
filesystem is just being mounted / remounted read-write and thus the
root directory cannot change anyway but it's definitely cleaner with
i_mutex.

Reported-by: Bastien ROUCARIES <roucaries.bastien@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 2 insertions, 0 deletions

diff --git a/fs/quota/dquot.c b/fs/quota/dquot.c
index eb5a755718f6..cd6bb9a33c13 100644
--- a/fs/quota/dquot.c
+++ b/fs/quota/dquot.c
@@ -2164,7 +2164,9 @@ int vfs_quota_on_mount(struct super_block *sb, char *qf_name,
         struct dentry *dentry;
         int error;
 
+        mutex_lock(&sb->s_root->d_inode->i_mutex);
         dentry = lookup_one_len(qf_name, sb->s_root, strlen(qf_name));
+        mutex_unlock(&sb->s_root->d_inode->i_mutex);
         if (IS_ERR(dentry))
                 return PTR_ERR(dentry);