On Fri, Feb 27, 2015 at 08:14:47AM -0500, Prarit Bhargava wrote: > On 02/27/2015 07:46 AM, Naoya Horiguchi wrote: > > Hi Prarit, > > > > On Fri, Feb 27, 2015 at 06:09:52AM -0500, Prarit Bhargava wrote: > > ... > >> > @@ -157,6 +160,11 @@ void native_machine_crash_shutdown(struct pt_regs > >> > *regs) > >> > /* The kernel is broken so disable interrupts */ > >> > local_irq_disable(); > >> > > >> > + /* > >> > + * We can't expect MCE handling to work any more, so turn it off. > >> > + */ > >> > + cpu_emergency_mce_disable(); > >> > >> What if the system is actually having problems with MCE errors -- which are > >> leading to system panics of some sort. Do you *really* want the system to > >> continue on at that point? > > > > Yes, when running the above code, the system doesn't run any business logic, > > so no worry about consuming broken data caused by HW errors. > > And what we really want to get is any kind of information to find out what > > caused the 1st panic, which are likely to be contained in kdump data. > > So I think it's justified to improve the success rate of kdump by continuing > > the operation here. > > I looked into it a bit further -- IIUC (according to the Intel spec) disabling > MCE this way will result in power cycle of the system if an MCE is detected. > So > I guess it isn't a worry for Intel. If anyone from AMD can hazard a guess > what > happens in their case it would be appreciated. > > I still don't like this approach all that much as a corrected non-fatal error > is > something I would want to know about as an admin, but that risk is mitigated > by > BMC and system monitoring hardware.
Generally corrected non-fatal errors are not reported via MCE but via CMCI, so not affected by sync timeout problem (they should be logged by mcelog after reboot in a normal manner.) But as for BMC/FW/HW logging, I'm not 100% sure that such logging mechanisms still work when disabling CR4.MCE, so I might need reconsider this approach. > >But the MCE handler is still enabled after that, so > >if MCE happens and broadcasts around CPUs after the main thread starts the > >2nd kernel (which might not start MCE yet, or might decide not to start MCE,) > >MCE handler runs only on the other CPUs (not on the main thread,) leading to > >kernel panic with MCE synchronization. > > Not having looked at the code (and relying on your description) -- there is no > way to disable the MCE handler? We have the way, as Tony suggesting in another email. And I feel like moving back to that approach in the next version. Thanks, Naoya Horiguchi-- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
