Re: [PATCH] nfs lockd: detect grace_list corruption

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

J. Bruce Fields said the following on 2009-5-7 4:32:
> 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?
> 

Yeah, the following fix is OK to me, although it only fixed
"start_grace again after start_grace" case.

The bug about "quit lockd without end_grace", which I encountered before
incidentally, maybe is still there.

> --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;
>  		}
>  
>