Re: [PATCH 2.6.10-mm2] Fix preemption race [1/3] (Core)

[Thomas Gleixner]

On Mon, 2005-01-10 at 10:15, Ingo Molnar wrote:
> * tglx@xxxxxxxxxxxxx <tglx@xxxxxxxxxxxxx> wrote:
> 
> > The idle-thread-preemption-fix.patch introduced a race, which is not
> > critical, but might give us an extra turn through the scheduler. When
> > interrupts are reenabled in entry.c and an interrupt occures before we
> > reach the add_preempt_schedule() in preempt_schedule we get
> > rescheduled again in the return from interrupt path.
> 
> i agree that there's a race. I solved this in the -RT patchset a couple
> of weeks ago, but in a different wasy. I introduced the
> preempt_schedule_irq() function and this solves the problem via keeping
> the whole IRQ-preemption path irqs-off. This has the advantage that if
> an IRQ signals preemption of a task and the kernel is immediately
> preemptable then we are able to hit that task atomically without
> re-enabling IRQs again. I'll split out this patch - can you see any
> problems with the preempt_schedule_irq() approach?

No.
I did not look into your RT patch for this, but please have a look at
RMK's ARM code, as he is doing some sanity check on
thread_info->preemption down there.

tglx


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