Re: [PATCH] nfs lockd: detect grace_list corruption

[Wang Chen <wangchen@cn.fujitsu.com>]

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().

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