On (12/10/18 16:57), Petr Mladek wrote: > > > (masked out) and on panic_cpu disables only SDEI (interrupts from firmware, > > > if I got it right); so it seems that arm64 can handle IRQs after panic. And > > > if there are platforms that handle IRQ (including sysrq) after panic, then > > > both options - making printk a noop or keeping local irqs off - maybe can > > > cause some problems. Or maybe not. We better ask arch people. > > > > Yes, this is very valid concern. And after Petr and you raised it, I did > > some experiments with 3 x86 platforms at my hand, one Apollolake IOT device > > with serial console, one IvyBridge laptop and one Kabylake NUC, the magic key > > all works well before panic, and fails after panic. But I did remember the > > PageUp/PageDown key worked on some laptop years ago. And you actually raised a > > good question: what do we expect for the post-panic kernel? > > I am not sure why it does not work. But it would be nice if sysrq > worked. Absolutely. [..] > I still think that calming down printk() is acceptable when > it can be restored from sysrq. I would agree; peeking one of the two solutions, printk patch is probably preferable. > I think that only few people might be interested into debugging > post-panic problems. We could print a warning for them about > that printk() has got disabled. Dunno. This _maybe_ (speculation!) can upset folks on those platforms that have sysrq working after panic. printk is a common code. I'm probably missing a lot of things here, but just in case, I'm not sure at which point the idea of patching some files under arch/x86 directory was ruled out and why. -ss
