Re: [Xen-devel] [PATCH] x86/HPET: mask interrupt while changing affinity

[Keir Fraser <keir@xxxxxxx>]

On 20/03/2013 13:38, "Jan Beulich" <JBeulich@xxxxxxxx> wrote:

>>>> On 20.03.13 at 12:55, Sander Eikelenboom <linux@xxxxxxxxxxxxxx> wrote:
>> Close but not entirely ;)
> 
> Close to not crashing, maybe, but whether this really helps with your
> problem is still entirely unclear.
> 
>> See attached serial log
> 
> Okay, I wasn't even aware of that assertion in _spin_lock_irq().
> 
> Keir, do you really think this is necessary?

You are more cunning than some others. ;) I'm pretty confident those
spinlock assertions save us from real bugs. Also I'd rather have blindingly
obvious code here than slightly faster code.

 -- Keir

> In the prior patch
> version, handle_hpet_broadcast() had a flow like this
> 
>     spin_lock_irqsave();
>     ...
>     spin_unlock_irqrestore();
>     ...
>     if ( next_event != STIME_MAX )
>     {
>         spin_lock_irq();
>         ...
>         spin_unlock_irqrestore();
>     }
> 
> avoiding the saving of the flags in the second lock acquire. Said
> assertion makes it impossible to do this.
> 
> Sander, in any case, attached a fixed version of the patch (I had
> to guess which of the two spin_lock_irq() calls it was, as the log
> was incomplete in that the stack trace got dropped, but am pretty
> positive that it was the one in handle_hpet_broadcast()).
> 
> Jan
> 



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