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. >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? P. -- 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/
