Messages in this thread | | | Subject | Re: [RFC][PATCH] IRQ: Fix oneshot irq race between irq_finalize_oneshot and handle_level_irq | From | Valdis.Kletnieks@vt ... | Date | Tue, 09 Mar 2010 11:59:05 -0500 |
| |
On Tue, 09 Mar 2010 08:58:11 +0100, Thomas Gleixner said: > 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.
What stops the thread from concurrently running on another CPU and racing that way? I'm an idiot, use small words. :) [unhandled content-type:application/pgp-signature] | |