Re: [PATCH] nfs lockd: detect grace_list corruption

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

On Wed, May 06, 2009 at 05:17:20PM +0800, Wang Chen wrote:
> J. Bruce Fields said the following on 2009-4-25 7:12:
> > On Fri, Apr 24, 2009 at 11:09:44AM +0800, Wang Chen wrote:
> >> Although I can't reproduce it now, it really happened that some lock manager
> >> started grace period but didn't end it.
> >> This causes an lm entry be left in grace_list, and when service nfs restart,
> >> the same lm will be added again into the list.
> >> As you know, adding an entry, which is in the list, to a list will leads to
> >> list corruption.
> > 
> > I'd really like to understand why locks_end_grace() isn't being called.
> > I'm probably overlooking something obvious, but I just can't see how
> > lockd or nfsd can be shut down right now without locks_end_grace() being
> > called.
> > 
> 
> Me neither can figure out why locks_end_grace() isn't being called.
> 
> But do locks_start_grace() twice can trigger this warning too.
> You can do
> 1. service nfs restart
> 2. (immediately) kill -s SIGKILL lockd
> this can trigger
> ---
> lockd(void *vrqstp)
> ...
> 		if (signalled()) {
> 			flush_signals(current);
> 			if (nlmsvc_ops) {
> 				nlmsvc_invalidate_all();
> 				set_grace_period();
> ---
> and makes locks_start_grace() be called twice without locks_end_grace().

Ah-hah!

> So I still suggest to do something to protect the lm list. :)

I wouldn't be opposed to a simple WARN_ON(!list_empty()) in
locks_start_grace(), but I'm mainly worried about fixing the original
bug.  How about the following?

--b.

diff --git a/fs/lockd/svc.c b/fs/lockd/svc.c
index abf8388..1a54ae1 100644
--- a/fs/lockd/svc.c
+++ b/fs/lockd/svc.c
@@ -104,6 +104,16 @@ static void set_grace_period(void)
 	schedule_delayed_work(&grace_period_end, grace_period);
 }
 
+static void restart_grace(void)
+{
+	if (nlmsvc_ops) {
+		cancel_delayed_work_sync(&grace_period_end);
+		locks_end_grace(&lockd_manager);
+		nlmsvc_invalidate_all();
+		set_grace_period();
+	}
+}
+
 /*
  * This is the lockd kernel thread
  */
@@ -149,10 +159,7 @@ lockd(void *vrqstp)
 
 		if (signalled()) {
 			flush_signals(current);
-			if (nlmsvc_ops) {
-				nlmsvc_invalidate_all();
-				set_grace_period();
-			}
+			restart_grace();
 			continue;
 		}