linux-kernel - Re: [PATCH v3 1/1] kexec: dump kmessage before machine

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Date:   Fri, 19 Mar 2021 14:31:38 -0500
From:   Tyler Hicks <tyhicks@...ux.microsoft.com>
To:     Pavel Tatashin <pasha.tatashin@...een.com>
Cc:     jmorris@...ei.org, sashal@...nel.org, pmladek@...e.com,
        ebiederm@...ssion.com, keescook@...omium.org, anton@...msg.org,
        ccross@...roid.com, tony.luck@...el.com, kexec@...ts.infradead.org,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH v3 1/1] kexec: dump kmessage before machine_kexec

On 2021-03-19 15:23:26, 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>
> Reviewed-by: Petr Mladek <pmladek@...e.com>
> Reviewed-by: Bhupesh Sharma <bhsharma@...hat.com>

Reviewed-by: Tyler Hicks <tyhicks@...ux.microsoft.com>

Tyler

> Acked-by: Baoquan He <bhe@...hat.com>
> ---
>  kernel/kexec_core.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/kernel/kexec_core.c b/kernel/kexec_core.c
> index a0b6780740c8..6ee4a1cf6e8e 100644
> --- a/kernel/kexec_core.c
> +++ b/kernel/kexec_core.c
> @@ -37,6 +37,7 @@
>  #include <linux/compiler.h>
>  #include <linux/hugetlb.h>
>  #include <linux/objtool.h>
> +#include <linux/kmsg_dump.h>
>  
>  #include <asm/page.h>
>  #include <asm/sections.h>
> @@ -1179,6 +1180,7 @@ int kernel_kexec(void)
>  		machine_shutdown();
>  	}
>  
> +	kmsg_dump(KMSG_DUMP_SHUTDOWN);
>  	machine_kexec(kexec_image);
>  
>  #ifdef CONFIG_KEXEC_JUMP
> -- 
> 2.25.1
>