Re: [Xen-devel] [Patch] don't spin with irq disabled

[Juergen Gross <juergen.gross@xxxxxxxxxxxxxxxxxxx>]

Jan Beulich wrote:
>>>> Juergen Gross <juergen.gross@xxxxxxxxxxxxxxxxxxx> 26.03.09 10:00 >>>
>> Attached patch reduces interrupt latency in lock handling.
>> spin_lock_irq and spin_lock_irqsave used to turn off IRQs and then tried to
>> get the lock. If the lock was already held, waiting for the lock was done 
>> with
>> IRQs still off.
>> The patch reenables IRQs during the wait loop.
> 
> This is wrong - you must not enable interrupts if they weren't enabled upon
> entry to these two functions.

spin_lock_irq disables always IRQs. spin_unlock_irq enables always IRQs. They
are always used in pairs, so IRQs should always be enabled on entry of
spin_lock_irq.
I'm not enabling IRQs unconditionally in spin_lock_irqsave, of course, but use
the flags value saved before...

Did I miss something? Or did you refer only to my inexact comment above?


Juergen

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Juergen Gross                             Principal Developer
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