Re: [PATCH] arm64:kexec: have own crash_smp_send_stop() for crash dump for nonpanic cores

[AKASHI Takahiro]

On Fri, Aug 04, 2017 at 11:38:16AM +0100, James Morse wrote:
> Hi Hoeun,
> 
> On 04/08/17 08:02, Hoeun Ryu wrote:
> >  Commit 0ee5941 : (x86/panic: replace smp_send_stop() with kdump friendly
> > version in panic path) introduced crash_smp_send_stop() which is a weak
> > function and can be overriden by architecture codes to fix the side effect
> > caused by commit f06e515 : (kernel/panic.c: add "crash_kexec_post_
> > notifiers" option).
> 
> If I've understood correctly: if we boot with this option core code doesn't use
> our machine_crash_shutdown(), and instead calls crash_smp_send_stop(), which we

No. Machine_crash_shutdown() is always called, but at that time,
all the cpus other than the crashing cpu have already died in this case.

> don't have, so it uses the default smp_send_stop(), which doesn't save the regs.
> 
> Thanks for catching this!
> 
> 
> Could we rename smp_send_crash_stop() crash_smp_send_stop() and add the
> called-twice logic there? They are similar enough that I'm getting them muddled
> already!
> 

Nice.

-Takahiro AKASHI

> 
> Thanks,
> 
> James
> 
> 
> >  ARM64 architecture uses the weak version function and the problem is that
> > the weak function simply calls smp_send_stop() which makes other CPUs
> > offline and takes away the chance to save crash information for nonpanic
> > CPUs in machine_crash_shutdown() when crash_kexec_post_notifiers kernel
> > option is enabled.
> > 
> >  Calling smp_send_crash_stop() in the function is useless because all
> > nonpanic CPUs are already offline by smp_send_stop() in this case and
> > smp_send_crash_stop() only works against online CPUs.
> > 
> >  The result is that /proc/vmcore is not available with the error messages;
> > "Warning: Zero PT_NOTE entries found", "Kdump: vmcore not initialized".
> > 
> >  crash_smp_send_stop() is implemented for ARM64 architecture to fix this
> > problem and the function (strong symbol version) saves crash information
> > for nonpanic CPUs using smp_send_crash_stop() and machine_crash_shutdown()
> > tries to save crash information for nonpanic CPUs only when
> > crash_kexec_post_notifiers kernel option is disabled.
> 
>