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>

2 files changed, 16 insertions, 6 deletions

diff --git a/fs/lockd/svclock.c b/fs/lockd/svclock.c
index b56d439bad82..9cfced65d4a2 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 *block, int unlock)
                 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 *file, struct nlm_lock *lock)
 
         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 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);