Author: J. Bruce Fields <bfields@fieldses.org>
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>
---

 fs/lockd/svclock.c |   15 ++++++++++-----
 fs/locks.c         |    7 ++++++-
 include/linux/fs.h |    2 +-
 3 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/fs/lockd/svclock.c b/fs/lockd/svclock.c
index b56d439..9cfced6 100644
--- a/fs/lockd/svclock.c
+++ b/fs/lockd/svclock.c
@@ -227,25 +227,27 @@ failed:
  * It is the caller's responsibility to check whether the file
  * can be closed hereafter.
  */
-static void
+static int
 nlmsvc_delete_block(struct nlm_block *block, int unlock)
 {
 	struct file_lock	*fl = &block->b_call.a_args.lock.fl;
 	struct nlm_file		*file = block->b_file;
 	struct nlm_block	**bp;
+	int status = 0;
 
 	dprintk("lockd: deleting block %p...\n", block);
 
 	/* Remove block from list */
 	nlmsvc_remove_block(block);
-	posix_unblock_lock(file->f_file, fl);
+	if (unlock)
+		status = posix_unblock_lock(file->f_file, fl);
 
 	/* If the block is in the middle of a GRANT callback,
 	 * don't kill it yet. */
 	if (block->b_incall) {
 		nlmsvc_insert_block(block, NLM_NEVER);
 		block->b_done = 1;
-		return;
+		return status;
 	}
 
 	/* Remove block from file's list of blocks */
@@ -260,6 +262,7 @@ nlmsvc_delete_block(struct nlm_block *bl
 		nlm_release_host(block->b_host);
 	nlmclnt_freegrantargs(&block->b_call);
 	kfree(block);
+	return status;
 }
 
 /*
@@ -270,6 +273,7 @@ int
 nlmsvc_traverse_blocks(struct nlm_host *host, struct nlm_file *file, int action)
 {
 	struct nlm_block	*block, *next;
+	/* XXX: Will everything get cleaned up if we don't unlock here? */
 
 	down(&file->f_sema);
 	for (block = file->f_blocks; block; block = next) {
@@ -439,6 +443,7 @@ u32
 nlmsvc_cancel_blocked(struct nlm_file *file, struct nlm_lock *lock)
 {
 	struct nlm_block	*block;
+	int status = 0;
 
 	dprintk("lockd: nlmsvc_cancel(%s/%ld, pi=%d, %Ld-%Ld)\n",
 				file->f_file->f_dentry->d_inode->i_sb->s_id,
@@ -449,9 +454,9 @@ nlmsvc_cancel_blocked(struct nlm_file *f
 
 	down(&file->f_sema);
 	if ((block = nlmsvc_lookup_block(file, lock, 1)) != NULL)
-		nlmsvc_delete_block(block, 1);
+		status = nlmsvc_delete_block(block, 1);
 	up(&file->f_sema);
-	return nlm_granted;
+	return status ? nlm_lck_denied : nlm_granted;
 }
 
 /*
diff --git a/fs/locks.c b/fs/locks.c
index 75650d5..fb32d62 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);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index cc35b6a..a947734 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -729,7 +729,7 @@ extern struct file_lock *posix_test_lock
 extern int posix_lock_file(struct file *, struct file_lock *);
 extern int posix_lock_file_wait(struct file *, struct file_lock *);
 extern void posix_block_lock(struct file_lock *, struct file_lock *);
-extern void posix_unblock_lock(struct file *, struct file_lock *);
+extern int posix_unblock_lock(struct file *, struct file_lock *);
 extern int posix_locks_deadlock(struct file_lock *, struct file_lock *);
 extern int flock_lock_file_wait(struct file *filp, struct file_lock *fl);
 extern int __break_lease(struct inode *inode, unsigned int flags);