Messages in this thread |  | | | Date | Tue, 9 Mar 2010 08:58:11 +0100 (CET) | | From | Thomas Gleixner <> | | Subject | Re: [RFC][PATCH] IRQ: Fix oneshot irq race between irq_finalize_oneshot and handle_level_irq |
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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.
Thanks,
tglx
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