On (12/05/18 11:57), Sergey Senozhatsky wrote: > On (12/05/18 10:47), Feng Tang wrote: > > > > Btw, just FYI, I just tried the sysrq (using minicom CTL + A + F + 'magic key'), > > it works with system is running, but failed after I trigger a panic, I will > > check more though I'm not very familiar with sysrq yet. OK... So, apparently, what's happening is panic() calls smp_send_stop(). And smp_send_stop()->native_stop_other_cpus() on x86 disables local APIC. So no fun anymore. If I keep APIC enabled on panic CPU, then I have my keyboard working, including PageUp-PageDown scrolling, sysrq handling, and so on. I think I'm not the only one who'd want scrollback to work after panic (yes, fremebuffer for debugging). Andi Kleen [1] wrote (Cc-ed): : Oops/warnings are getting longer and longer, often scrolling away : from the screen, and if the kernel crashes backscroll does not work : anymore, so precious information is lost. PeterZ, for those folks who sometimes have to use framebuffer for debugging (just a trivial "let me scrollback and see the panic backtrace") and not always have access to serial console, can we have local APIC enabled on the panic_cpu? Or is it a terrible thing to ask for? [1] https://lore.kernel.org/lkml/878tcvt592.fsf@xxxxxxxxxxxxxxx/T/#u -ss
