On 05/23/2014 08:42 PM, Peter Zijlstra wrote: > On Fri, May 23, 2014 at 08:15:35PM +0530, Srivatsa S. Bhat wrote: >>>> + * During CPU offline, we don't want the other CPUs to send >>>> + * IPIs to the active_cpu (the outgoing CPU) *after* it has >>>> + * disabled interrupts (because, then it will notice the IPIs >>>> + * only after it has gone offline). We can prevent this by >>>> + * making the other CPUs disable their interrupts first - that >>>> + * way, they will run the stop-machine code with interrupts >>>> + * disabled, and hence won't send IPIs after that point. > > That's complete nonsense, you can send IPIs all you want with interrupts > disabled. >
True, but that's not what the comment says. It says "you can't send IPIs because you are running the *stop-machine* loop, because the stop-machine loop doesn't send IPIs itself! The only possibility of sending IPIs from within stop-machine is if that CPU can takes an interrupt and the *interrupt handler* sends the IPI (like what the block layer used to do) - and we precisely avoid that possibility by disabling interrupts. So no IPIs will be sent beyond this point. Regards, Srivatsa S. Bhat -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
