NLM: don't unlock on cancel requests

 Currently when lockd gets an NLM_CANCEL request, it also does an unlock for
 the same range.  This is incorrect.

 The Open Group documentation says that "This procedure cancels an
 *outstanding* blocked lock request."  (Emphasis mine.)

 Also, consider a client that holds a lock on the first byte of a file, and
 requests a lock on the entire file.  If the client cancels that request
 (perhaps because the requesting process is signalled), the server shouldn't
 apply perform an unlock on the entire file, since that will also remove the
 previous lock that the client was already granted.

 Or consider a lock request that actually *downgraded* an exclusive lock to
 a shared lock.

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

1 files changed, 2 insertions, 11 deletions

diff --git a/fs/locks.c b/fs/locks.c
index 250ef53..75650d5 100644
--- a/fs/locks.c
+++ b/fs/locks.c
@@ -1961,19 +1961,10 @@ EXPORT_SYMBOL(posix_block_lock);
 void
 posix_unblock_lock(struct file *filp, struct file_lock *waiter)
 {
-	/* 
-	 * A remote machine may cancel the lock request after it's been
-	 * granted locally.  If that happens, we need to delete the lock.
-	 */
 	lock_kernel();
-	if (waiter->fl_next) {
+	if (waiter->fl_next)
 		__locks_delete_block(waiter);
-		unlock_kernel();
-	} else {
-		unlock_kernel();
-		waiter->fl_type = F_UNLCK;
-		posix_lock_file(filp, waiter);
-	}
+	unlock_kernel();
 }
 
 EXPORT_SYMBOL(posix_unblock_lock);