Messages in this thread | | | Date | Fri, 20 Jun 2014 11:41:27 -0400 | From | Boris Ostrovsky <> | Subject | Re: [PATCH] x86/mce: Don't unregister CPU hotplug notifier in error path |
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On 06/20/2014 11:23 AM, Borislav Petkov wrote: > On Fri, Jun 20, 2014 at 10:28:13AM -0400, Boris Ostrovsky wrote: >> Commit 9c15a24b038f4d8da93a2bc2554731f8953a7c17 (x86/mce: Improve >> mcheck_init_device() error handling) unregisters (or never registers) >> MCE's hotplug notifier if an error is encountered. > Well, mcheck_init_device() did encounter errors before that commit too, > can you please go into detail on how exactly you're triggering this? > Which error are you talking about exactly?
You can simulate this on baremetal by having, for example, misc_register() fail (just add 'err = -EOI' after the call). Or you can return an error right upon entry to mcheck_init_device() (I haven't tested that though).
Then, after you are booted do a couple of echo 0 > /sys/devices/system/cpu/cpu1/online echo 1 > /sys/devices/system/cpu/cpu1/online
Then sit still for about 10 minutes. I don't think any activity is necessary.
You are dead now. If you are lucky you may see messages about soft lockups or RCU stalls but often nothing.
> Lemme guess: some xen special handling which baremetal doesn't need.
Only in the sense that on Xen misc_register() often fails. But any failure on baremetal will result in the same behavior.
> >> Since unplugging a CPU would normally result in the notifier deleting >> MCE timer we are now left with the timer running if a CPU is removed on >> a system where mcheck_init_device() had failed. >> >> If we later hotplug this CPU back we add this timer again in >> mcheck_cpu_init()). Eventually the two timers start intefering with each >> other, causing soft lockups or system hangs. >> >> We should leave the notifier always on and, in fact, set it up early >> during the boot. > We do leave it always on - we only unregister it if we've encountered an > error.
Right. And I think we shouldn't because we leave undeleted timers.
-boris
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