On Fri, Feb 06, 2009 at 02:05:50PM -0700, Alex Chiang wrote: > * Luck, Tony <tony.luck@xxxxxxxxx>: > > > This is wrong because fixup_irqs calls migrate_irqs, and in > > > migrate_irqs, we use the cpu_online_map to: > > > > > > 1. look for interrupts on current CPU > > > 2. if we find one, move it to the first available CPU in > > > the cpu_online_map > > > > > > This means we can potentially migrate an interrupt off ourself > > > back to... ourself. Uh oh. > > > > Should we make migrate_irqs smarter then ... does any caller really > > expect that it would "migrate" the irq to the same cpu? > > The only thing migrate_irqs does is locate irqs that have their > CPU affinity set to the current CPU, and if so, changes the > affinity. > > We still have possible pending timer interrupts that we need to > handle, so I'm not seeing how changing the migrate_irqs > implementation (to avoid migrating to ourself) will handle that. > > On one hand, I think the only irq handler that can be called at > this point is our timer_interrupt, which doesn't seem to be using > any RCU APIs. > > On the other hand, if we really want to make sure that we're not > calling interrupt handlers with our CPU marked as 'offline', then > we need to fix ia64_process_pending_intr() so that we're not > firing our timer_interrupt with a NULL pt_regs. > > Add in to the mix that x86 seems to have the same assumption that > we do (that it's ok to call our timer interrupt handler even if > we're already marked as 'offline'). > > I'm leaning towards reverting Paul's previous commit entirely > because > > - migrate_platform_irqs() doesn't cause any interrupt > handlers to be fired by itself > > - it also uses cpu_online)map to find a new CPU to assign > CPEI to > > Thoughts? I would suggest at least a comment stating why it is safe to take the interrupts on a CPU marked offline. As to the eventual solution, you guys are the experts on your architecture. Thanx, Paul -- To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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