Re: [NLM] 2.6.27 broken

["J. Bruce Fields" <bfields@fieldses.org>]

On Tue, Dec 16, 2008 at 03:16:10PM -0500, bfields wrote:
> On Tue, Dec 16, 2008 at 08:43:52PM +0100, Miklos Szeredi wrote:
> > On Tue, 2008-12-16 at 12:39 -0500, J. Bruce Fields wrote:
> > > More precisely, it looks like this started with
> > > 
> > > 	bde74e4bc64415b142e "locks: add special return value for
> > > 		asynchronous locks"
> > > 
> > > But I haven't had the chance to look any harder yet.  Miklos?  Is this
> > > easy for you to reproduce?
> > 
> > Not immediately, at the moment I don't have NFS set up.  But if you
> > don't beat me to it, I'll look into this.
> 
> OK, thanks.  I'll take another look too when I get the chance, so let me
> know of any partial result.
> 
> It may just for example be returning the wrong error to the client on an
> nlm blocking lock request, so that the client assumes the lock is gone
> and goes away rather than waiting for a grant request.

Sorry, I've gotten a bit backlogged, but I finally got back to this.  If
there's no objections, the following is what I intend to submit.

--b.

commit cb8b864ea6addd3a3e72fe835aafecec63f06cbd
Author: J. Bruce Fields <bfields-+qGSg9AQ1cLTsXDwO4sDpg@public.gmane.org>
Date:   Wed Feb 4 17:35:38 2009 -0500

    lockd: fix regression in lockd's handling of blocked locks
    
    If a client requests a blocking lock, is denied, then requests it again,
    then here in nlmsvc_lock() we will call vfs_lock_file() without FL_SLEEP
    set, because we've already queued a block and don't need the locks code
    to do it again.
    
    But that means vfs_lock_file() will return -EAGAIN instead of
    FILE_LOCK_DENIED.  So we still need to translate that -EAGAIN return
    into a nlm_lck_blocked error in this case, and put ourselves back on
    lockd's block list.
    
    The bug was introduced by bde74e4bc64415b1 "locks: add special return
    value for asynchronous locks".
    
    Thanks to From: Frank van Maarseveen for the report; his original test
    case was essentially
    
    	for i in `seq 30`; do flock /nfsmount/foo sleep 10 & done
    
    Cc: Frank van Maarseveen <frankvm@frankvm.com>
    Cc: Miklos Szeredi <mszeredi@suse.cz>
    Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>

diff --git a/fs/lockd/svclock.c b/fs/lockd/svclock.c
index 6063a8e..763b78a 100644
--- a/fs/lockd/svclock.c
+++ b/fs/lockd/svclock.c
@@ -427,7 +427,7 @@ nlmsvc_lock(struct svc_rqst *rqstp, struct nlm_file *file,
 			goto out;
 		case -EAGAIN:
 			ret = nlm_lck_denied;
-			goto out;
+			break;
 		case FILE_LOCK_DEFERRED:
 			if (wait)
 				break;
@@ -443,6 +443,10 @@ nlmsvc_lock(struct svc_rqst *rqstp, struct nlm_file *file,
 			goto out;
 	}
 
+	ret = nlm_lck_denied;
+	if (!wait)
+		goto out;
+
 	ret = nlm_lck_blocked;
 
 	/* Append to list of blocked */