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SubjectRe: scheduler: IRQs disabled over context switches
On Sun, May 23, 2004 at 04:04:39PM -0700, Davide Libenzi wrote:
> On Sun, 23 May 2004, Russell King wrote:
> > Not quite - look harder. They use spin_unlock_irq in finish_arch_switch
> > rather than prepare_arch_switch.
>
> Hmm, they do indeed. Hmm, if we release the rq lock before the ctx switch,
> "prev" (the real one) will result not running since we already set
> "rq->curr" to "next" (and we do not hold "prev->switch_lock").

We do hold prev->switch_lock - we hold it all the time that the thread
is running. Consider what prepare_arch_switch() is doing - it's taking
the next threads switch_lock. It only gets released _after_ we've
switched away from that thread.

So I think your analysis is flawed.

--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
maintainer of: 2.6 PCMCIA - http://pcmcia.arm.linux.org.uk/
2.6 Serial core
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