linux-kernel - Re: [PATCH] kexec: dump kmessage before machine

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Message-ID: <202006051426.4F06C696@keescook>
Date:   Fri, 5 Jun 2020 14:26:36 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Pavel Tatashin <pasha.tatashin@...een.com>
Cc:     jmorris@...ei.org, sashal@...nel.org, pmladek@...e.com,
        ebiederm@...ssion.com, anton@...msg.org, ccross@...roid.com,
        tony.luck@...el.com, kexec@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] kexec: dump kmessage before machine_kexec

On Fri, Jun 05, 2020 at 03:46:42PM -0400, Pavel Tatashin wrote:
> kmsg_dump(KMSG_DUMP_SHUTDOWN) is called before
> machine_restart(), machine_halt(), machine_power_off(), the only one that
> is missing is  machine_kexec().
> 
> The dmesg output that it contains can be used to study the shutdown
> performance of both kernel and systemd during kexec reboot.
> 
> Here is example of dmesg data collected after kexec:
> 
> root@...at-cp22:~# cat /sys/fs/pstore/dmesg-ramoops-0 | tail
> ...
> <6>[   70.914592] psci: CPU3 killed (polled 0 ms)
> <5>[   70.915705] CPU4: shutdown
> <6>[   70.916643] psci: CPU4 killed (polled 4 ms)
> <5>[   70.917715] CPU5: shutdown
> <6>[   70.918725] psci: CPU5 killed (polled 0 ms)
> <5>[   70.919704] CPU6: shutdown
> <6>[   70.920726] psci: CPU6 killed (polled 4 ms)
> <5>[   70.921642] CPU7: shutdown
> <6>[   70.922650] psci: CPU7 killed (polled 0 ms)
> 
> Signed-off-by: Pavel Tatashin <pasha.tatashin@...een.com>

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook