Messages in this thread | | | Date | Tue, 28 Jan 2014 13:09:14 +0100 | From | Jan Kiszka <> | Subject | Re: [PATCH] x86: Plug racy xAPIC access of CPU hotplug code |
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On 2014-01-28 12:55, Ingo Molnar wrote: > > * Jan Kiszka <jan.kiszka@siemens.com> wrote: > >> On 2014-01-27 21:22, Andi Kleen wrote: >>> On Mon, Jan 27, 2014 at 08:14:06PM +0100, Jan Kiszka wrote: >>>> apic_icr_write and its users in smpboot.c were apparently written under >>>> the assumption that this code would only run during early boot. But >>>> nowadays we also execute it when onlining a CPU later on while the >>>> system is fully running. That will make wakeup_cpu_via_init_nmi and, >>>> thus, also native_apic_icr_write run in plain process context. If we >>>> migrate the caller to a different CPU at the wrong time or interrupt it >>>> and write to ICR/ICR2 to send unrelated IPIs, we can end up sending >>>> INIT, SIPI or NMIs to wrong CPUs. >>>> >>>> Fix this by disabling interrupts during the write to the ICR halves and >>>> disable preemption around waiting for ICR availability and using it. >>> >>> If you just want to disable migration use get_cpu()/put_cpu() >> >> Fine with me if that is now preferred. Will that be the upstream way of >> -rt's migrate_disable()? > > Your original patch is fine, the suggestion to do ICR accesses with > just preemption disabled is crap and is really asking for trouble: if > some IRQ comes in at that point after all then it might cause all > sorts of hard to debug problems (hangs, delays, missed IPIs, etc.).
Of course, we still need irqs off during ICR writes. I thought Andi was just suggesting to replace preempt_disable with get_cpu, maybe to document why we are disabling preemption here.
Jan
-- Siemens AG, Corporate Technology, CT RTC ITP SES-DE Corporate Competence Center Embedded Linux
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