Messages in this thread | | | From | David Brownell <> | Subject | Re: [patch/rfc 1/2] GENIRQ: add handle_threaded_irq() flow handler | Date | Wed, 18 Mar 2009 11:31:22 -0700 |
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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. -- 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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