linux-kernel - Re: [PATCH] arm64:kexec: have own crash_smp_send

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Date:   Fri, 04 Aug 2017 11:38:16 +0100
From:   James Morse <james.morse@....com>
To:     Hoeun Ryu <hoeun.ryu@...il.com>
CC:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        AKASHI Takahiro <takahiro.akashi@...aro.org>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64:kexec: have own crash_smp_send_stop() for crash
 dump for nonpanic cores

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
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!


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.