cifs: use posix_unblock_lock instead of locks_delete_block

commit 66189be74 (CIFS: Fix VFS lock usage for oplocked files) exported
the locks_delete_block symbol. There's already an exported helper
function that provides this capability however, so make cifs use that
instead and turn locks_delete_block back into a static function.

Note that if fl->fl_next == NULL then this lock has already been through
locks_delete_block(), so we should be OK to ignore an ENOENT error here
and simply not retry the lock.

Cc: Pavel Shilovsky <piastryyy@gmail.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Acked-by: J. Bruce Fields <bfields@fieldses.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/cifs/file.c

@@ -999,7 +999,7 @@ try_again:
 		rc = wait_event_interruptible(flock->fl_wait, !flock->fl_next);
 		if (!rc)
 			goto try_again;
-		locks_delete_block(flock);
+		posix_unblock_lock(flock);
 	}
 	return rc;
 }

fs/locks.c

@@ -496,13 +496,12 @@ static void __locks_delete_block(struct file_lock *waiter)
 
 /*
  */
-void locks_delete_block(struct file_lock *waiter)
+static void locks_delete_block(struct file_lock *waiter)
 {
 	lock_flocks();
 	__locks_delete_block(waiter);
 	unlock_flocks();
 }
-EXPORT_SYMBOL(locks_delete_block);
 
 /* Insert waiter into blocker's block list.
  * We use a circular list so that processes can be easily woken up in

include/linux/fs.h

@@ -1006,7 +1006,6 @@ extern int vfs_setlease(struct file *, long, struct file_lock **);
 extern int lease_modify(struct file_lock **, int);
 extern int lock_may_read(struct inode *, loff_t start, unsigned long count);
 extern int lock_may_write(struct inode *, loff_t start, unsigned long count);
-extern void locks_delete_block(struct file_lock *waiter);
 extern void lock_flocks(void);
 extern void unlock_flocks(void);
 #else /* !CONFIG_FILE_LOCKING */
@@ -1150,10 +1149,6 @@ static inline int lock_may_write(struct inode *inode, loff_t start,
 	return 1;
 }
 
-static inline void locks_delete_block(struct file_lock *waiter)
-{
-}
-
 static inline void lock_flocks(void)
 {
 }