NLM: Further cancel fixes

 If the server receives an NLM cancel call and finds no waiting lock to
 cancel, then chances are the lock has already been applied, and the client
 just hadn't yet processed the NLM granted callback before it sent the
 cancel.

 The Open Group text, for example, perimts a server to return either success
 (LCK_GRANTED) or failure (LCK_DENIED) in this case.  But returning an error
 seems more helpful; the client may be able to use it to recognize that a
 race has occurred and to recover from the race.

 So, modify the relevant functions to return an error in this case.

 Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
 Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

1 files changed, 6 insertions, 1 deletions

diff --git a/fs/locks.c b/fs/locks.c
index 75650d52fe60..fb32d6218e21 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1958,13 +1958,18 @@ EXPORT_SYMBOL(posix_block_lock);
  *
  *	lockd needs to block waiting for locks.
  */
-void
+int
 posix_unblock_lock(struct file *filp, struct file_lock *waiter)
 {
+	int status = 0;
+
 	lock_kernel();
 	if (waiter->fl_next)
 		__locks_delete_block(waiter);
+	else
+		status = -ENOENT;
 	unlock_kernel();
+	return status;
 }
 
 EXPORT_SYMBOL(posix_unblock_lock);