Re: [PATCH 1/5] Protect irq_sources_bitmap by kvm->lock instead of kvm->irq_lock

[Gleb Natapov <gleb@redhat.com>]

On Mon, Jul 13, 2009 at 11:03:56AM -0400, Gregory Haskins wrote:
> Gleb Natapov wrote:
> > On Mon, Jul 13, 2009 at 10:29:02AM -0400, Gregory Haskins wrote:
> >   
> >> Gleb Natapov wrote:
> >>     
> >>> diff --git a/virt/kvm/irq_comm.c b/virt/kvm/irq_comm.c
> >>> index 6c57e46..ce8fcd3 100644
> >>> --- a/virt/kvm/irq_comm.c
> >>> +++ b/virt/kvm/irq_comm.c
> >>> @@ -210,7 +210,8 @@ int kvm_request_irq_source_id(struct kvm *kvm)
> >>>  	unsigned long *bitmap = &kvm->arch.irq_sources_bitmap;
> >>>  	int irq_source_id;
> >>>  
> >>> -	mutex_lock(&kvm->irq_lock);
> >>> +	WARN_ON(!mutex_is_locked(&kvm->lock));
> >>>   
> >>>       
> >> Shouldn't this be fatal?  (e.g. BUG_ON).  I know the usage between
> >> BUG/WARN is controversial, but it seems to me that something is
> >> completely broken if you expect it to be locked and its not.  Might as
> >> well fail the system, IMO.
> >>
> >>     
> > Well I don't really care but we have WARN_ON() in the code currently.
> >   
> 
> Well, that is perhaps unfortunate, but not relevant.  I am not reviewing
> those patches ;)
> 
> > Besides the chances are good that even without locking around this
> > function nothing will break, so why kill host kernel?
> >   
> 
> The question to ask is: Is it legal to continue to run if the mutex is
> found unlocked?  If not, the offending caller should be found/fixed as
> early as possible IMO, and an oops should be sufficient to do so.  I
> think WARN_ON tends to gets overused/abused, so lets not perpetuate it
> simply because of precedence.
> 
I will have to end this particular thread about WARN_ON by stating
that Avi told me to put it there. I'll let him decide.

--
			Gleb.