linux-kernel - Re: [PATCH] drivers: hv: log when enabling crash_kexec_post

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Message-ID: <20220218131017.cmzirxxo2msppgy4@liuwe-devbox-debian-v2>
Date:   Fri, 18 Feb 2022 13:10:17 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
Cc:     Stephen Brennan <stephen.s.brennan@...cle.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drivers: hv: log when enabling crash_kexec_post_notifiers

On Thu, Feb 17, 2022 at 04:44:13PM +0000, Michael Kelley (LINUX) wrote:
> From: Stephen Brennan <stephen.s.brennan@...cle.com> Sent: Monday, February 14, 2022 5:38 PM
> > 
> > Recently I went down a rabbit hole looking at a race condition in
> > panic() on a Hyper-V guest. I assumed, since it was missing from the
> > command line, that crash_kexec_post_notifiers was disabled. Only after
> > a rather long reproduction and analysis process did I learn that Hyper-V
> > actually enables this setting unconditionally.
> > 
> > Users and debuggers alike would like to know when these things happen. I
> > think it would be good to print a message to the kernel log when this
> > happens, so that a grep for "crash_kexec_post_notifiers" shows relevant
> > results.
> 
> I'm OK with adding this output line.  However, you have probably
> seen the two other LKML threads [1] and [2] about reorganizing the
> panic notifiers to clearly distinguish between notifiers that always run
> vs. those controlled by "crash_kexec_post_notifiers".  If the changes
> proposed in those threads are submitted and accepted, it is likely that
> the kernel log message in this patch would become unnecessary.
> But since we don't know when those proposed changes might come
> to fruition, adding the message for now makes sense.
> 
> Reviewed-by: Michael Kelley <mikelley@...rosoft.com>

Applied to hyperv-next. Thanks.