Messages in this thread | | | Date | Wed, 18 Mar 2009 20:32:19 +0200 | From | Felipe Balbi <> | Subject | Re: [patch/rfc 1/2] GENIRQ: add handle_threaded_irq() flow handler |
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On Wed, Mar 18, 2009 at 07:31:22PM +0100, David Brownell wrote: > On Wednesday 18 March 2009, Felipe Balbi wrote: > > > + action = desc->action; > > > + if (unlikely(!action || (desc->status & IRQ_DISABLED))) > > > + goto out_unlock; > > > > you say below irqs are always enabled > > Right here they're always disabled by spin_lock_irq(). > The "below" follows spin_unlock_irq(), which re-enables > them to traverse that (locked) action list. > > > > so this branch is something we > > never want to happen. How about adding a WARN() then ? > > When some one says "irqs are enabled" they mean that, > local_irq_disable() or friends have not been called, > so for example a timer or other IRQ could arrive. > > The IRQ_DISABLED flag in an IRQ descriptor means > something different: "don't try *handling* this". > > That particular check is used in *ALL* flow handlers. > It guards against things like races in disable_irq() > paths, which could allow an IRQ that was in flight > to arrive "after" the IRQ was disabled. > > In the case of an IRQ enable/disable mask sitting > across an I2C bus boundary, it's particularly easy > to see how such a race might happen ... since both > the thread masking the IRQ, and the one handling it, > are subject to preemption and scheduling.
aha, I see. Thanks for the explanation ;-)
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