linux-kernel - Re: [PATCH v2 1/1] kexec: dump kmessage before machine

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Date:   Thu, 28 Jan 2021 16:43:51 -0500
From:   Pavel Tatashin <pasha.tatashin@...een.com>
To:     "Eric W. Biederman" <ebiederm@...ssion.com>
Cc:     James Morris <jmorris@...ei.org>, Sasha Levin <sashal@...nel.org>,
        Tyler Hicks <tyhicks@...ux.microsoft.com>,
        Petr Mladek <pmladek@...e.com>,
        Kees Cook <keescook@...omium.org>,
        Anton Vorontsov <anton@...msg.org>,
        Colin Cross <ccross@...roid.com>,
        Tony Luck <tony.luck@...el.com>,
        kexec mailing list <kexec@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/1] kexec: dump kmessage before machine_kexec

On Thu, Jan 28, 2021 at 3:01 PM Eric W. Biederman <ebiederm@...ssion.com> wrote:
>
> Pavel Tatashin <pasha.tatashin@...een.com> writes:
>
> > 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:
>
> As long was we keep kmsg_dump out of the crash_kexec path where
> it completely breaks kexec on panic this seems a reasonable thing to do.
> On the ordinary kernel_kexec path everything is expected to be working.

This is an ordinary kexec reboot path, not kdump.

>
> Is kmsg_dump expected to work after all of the device drivers
> are shut down?  Otherwise this placement of kmsg_dump is too late.

Yes it is. It is called after device_shutdown(); in all other places.


Thank you,
Pasha