quota: Fix deadlock during path resolution

As Al Viro pointed out path resolution during Q_QUOTAON calls to quotactl
is prone to deadlocks. We hold s_umount semaphore for reading during the
path resolution and resolution itself may need to acquire the semaphore
for writing when e. g. autofs mountpoint is passed.

Solve the problem by performing the resolution before we get hold of the
superblock (and thus s_umount semaphore). The whole thing is complicated
by the fact that some filesystems (OCFS2) ignore the path argument. So to
distinguish between filesystem which want the path and which do not we
introduce new .quota_on_meta callback which does not get the path. OCFS2
then uses this callback instead of old .quota_on.

CC: Al Viro <viro@ZenIV.linux.org.uk>
CC: Christoph Hellwig <hch@lst.de>
CC: Ted Ts'o <tytso@mit.edu>
CC: Joel Becker <joel.becker@oracle.com>
Signed-off-by: Jan Kara <jack@suse.cz>

1 files changed, 4 insertions, 1 deletions

diff --git a/include/linux/quota.h b/include/linux/quota.h
index 94c1f03b50eb..9a85412e0db6 100644
--- a/include/linux/quota.h
+++ b/include/linux/quota.h
@@ -322,9 +322,12 @@ struct dquot_operations {
         qsize_t *(*get_reserved_space) (struct inode *);
 };
 
+struct path;
+
 /* Operations handling requests from userspace */
 struct quotactl_ops {
-        int (*quota_on)(struct super_block *, int, int, char *);
+        int (*quota_on)(struct super_block *, int, int, struct path *);
+        int (*quota_on_meta)(struct super_block *, int, int);
         int (*quota_off)(struct super_block *, int);
         int (*quota_sync)(struct super_block *, int, int);
         int (*get_info)(struct super_block *, int, struct if_dqinfo *);