Messages in this thread | | | Date | Tue, 9 Mar 2010 16:08:00 +0800 | From | Yong Zhang <> | Subject | Re: [RFC][PATCH] IRQ: Fix oneshot irq race between irq_finalize_oneshot and handle_level_irq |
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On Tue, Mar 09, 2010 at 08:58:11AM +0100, Thomas Gleixner wrote: > On Tue, 9 Mar 2010, Lars-Peter Clausen wrote: > > > If the kernel has been compiled with preemtion support and handle_level_irq is > > called from process context for a oneshot irq there is a race between > > irq_finalize_oneshot and handle_level_irq which results in the irq not being > > unmasked after its handlers have been run. > > > > irq_finalize_oneshot is expected to unmask the irq after the threaded irq > > handler has been run. It only does so if IRQ_MASKED is set for the irqs status. > > IRQ_MASKED gets set in the lower part of handle_level_irq after handle_IRQ_event > > has been called. > > handle_IRQ_event will wakeup the oneshot irqs threaded handler and if the > > kernel has been build with preemption there is a chance that the threaded irq > > handler will finish before execution is returned to handle_level_irq. > > As a result irq_finalize_oneshot will not unmask the irq and handle_level_irq > > will set the IRQ_MASKED flag. Thus the irq will stay masked and stalls. > > > > In case of an race the call-graph would look like this: > > handle_level_irq > > |- mask_ack_irq > > |- handle_IRQ_event > > |- wake_up_process > > |- irq_thread > > |- action->thread_fn > > |- irq_finalize_oneshot # Does not unmask the irq > > |- # Set IRQ_MASKED status flag > > Errm, a thread _CANNOT_ preempt a hard interrupt handler.
But on SMP, an irq thread could run on another cpu, right?
Thanks, Yong
> > Thanks, > > tglx > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
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