linux-kernel - Re: kernel 2.6.39 (user mode linux) crashes (2.6.38 works fine)

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Message-ID: <1305907458.1465.23.camel@gandalf.stny.rr.com>
Date:	Fri, 20 May 2011 12:04:17 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Darren Hart <dvhart@...ux.intel.com>
Cc:	richard -rw- weinberger <richard.weinberger@...il.com>,
	Toralf Förster <toralf.foerster@....de>,
	LKML <linux-kernel@...r.kernel.org>,
	user-mode-linux-devel@...ts.sourceforge.net
Subject: Re: kernel 2.6.39 (user mode linux) crashes (2.6.38 works fine)

On Fri, 2011-05-20 at 08:55 -0700, Darren Hart wrote:

> I suspect Toralf is hitting the WARN_ON in __unqueue_futex:
> 
> 	if (WARN_ON(!q->lock_ptr || !spin_is_locked(q->lock_ptr)
> 			|| plist_node_empty(&q->list)))
> 
> Toralf, can you instrument that let us know which of conditions is
> triggering the WARN_ON? Something like the following should be adequate
> to get you the line number. I suspect it is plist_node_empty give the
> git bisect results you reported.
> 
> 
> diff --git a/kernel/futex.c b/kernel/futex.c
> index abd5324..7f31bca 100644
> --- a/kernel/futex.c
> +++ b/kernel/futex.c
> @@ -782,8 +782,11 @@ static void __unqueue_futex(struct futex_q *q)
>  {
>  	struct futex_hash_bucket *hb;
> 
> -	if (WARN_ON(!q->lock_ptr || !spin_is_locked(q->lock_ptr)
> -			|| plist_node_empty(&q->list)))
> +	if (WARN_ON(!q->lock_ptr))
> +		return;
> +	if (!spin_is_locked(q->lock_ptr))
> +		return;
> +	if (plist_node_empty(&q->list))
>  		return;
> 

Wait! This is where we need the WARN_ON_SMP(), do we have that patch in?

I think UML is UP, and that spin_is_locked() will always return false.

-- Steve


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