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

[Darren Hart <dvhart@linux.intel.com>]

On 05/20/2011 09:04 AM, Steven Rostedt wrote:
> 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;
>>
> 

Whoops, there should have been WARN_ON's in all the if blocks... duh.

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

Hrm, I thought he said he was on 2.6.39-rc-something. Those patches went
in pre 2.6.39-rc1 according to gitk.

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

-- 
Darren Hart
Intel Open Source Technology Center
Yocto Project - Linux Kernel