9p: Skip check for mandatory locks when unlocking

While investigating a bug, I came across a possible bug in v9fs. The
problem is similar to the one reported for NFS by ASANO Masahiro in
http://lkml.org/lkml/2005/12/21/334.

v9fs_file_lock() will skip locks on file which has mode set to 02666.
This is a problem in cases where the mode of the file is changed after
a process has obtained a lock on the file. Such a lock will be skipped
during unlock and the machine will end up with a BUG in
locks_remove_flock().

v9fs_file_lock() should skip the check for mandatory locks when
unlocking a file.

Signed-off-by: Sachin Prabhu <sprabhu@redhat.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>

diff --git a/fs/9p/vfs_file.c b/fs/9p/vfs_file.c
index 019f1cd8750b3b31a5b96109f29b7e8a1ea393df..df52d488d2a697ad917e53ee96428c7c2714ae98 100644 (file)
--- a/fs/9p/vfs_file.c
+++ b/fs/9p/vfs_file.c
@@ -114,7 +114,7 @@ static int v9fs_file_lock(struct file *filp, int cmd, struct file_lock *fl)
        P9_DPRINTK(P9_DEBUG_VFS, "filp: %p lock: %p\n", filp, fl);
 
        /* No mandatory locks */
-       if (__mandatory_lock(inode))
+       if (__mandatory_lock(inode) && fl->fl_type != F_UNLCK)
                return -ENOLCK;
 
        if ((IS_SETLK(cmd) || IS_SETLKW(cmd)) && fl->fl_type != F_UNLCK) {