Message-ID: <4753106d-b370-5393-2908-4067f3c306e5@igalia.com>
Date:   Sun, 26 Feb 2023 13:11:09 -0300
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Subject: Re: [PATCH v4] panic: Fixes the panic_print NMI backtrace setting
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To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     bhe@redhat.com, pmladek@suse.com, linux-kernel@vger.kernel.org,
        kexec@lists.infradead.org, dyoung@redhat.com,
        d.hatayama@jp.fujitsu.com, feng.tang@intel.com,
        hidehiro.kawai.ez@hitachi.com, keescook@chromium.org,
        mikelley@microsoft.com, vgoyal@redhat.com, kernel-dev@igalia.com,
        kernel@gpiccoli.net, stable@vger.kernel.org
References: <20230210203510.1734835-1-gpiccoli@igalia.com>
 <20230225214454.5eb25ff8a937a99d357c44ad@linux-foundation.org>
From:   "Guilherme G. Piccoli" <gpiccoli@igalia.com>
In-Reply-To: <20230225214454.5eb25ff8a937a99d357c44ad@linux-foundation.org>
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On 26/02/2023 02:44, Andrew Morton wrote:
> On Fri, 10 Feb 2023 17:35:10 -0300 "Guilherme G. Piccoli" <gpiccoli@igalia.com> wrote:
> [...] 
>> Notice that while at it, I got rid of the "crash_kexec_post_notifiers"
>> local copy in panic(). This was introduced by commit b26e27ddfd2a
>> ("kexec: use core_param for crash_kexec_post_notifiers boot option"),
>> but it is not clear from comments or commit message why this local copy
>> is required.
>>
>> My understanding is that it's a mechanism to prevent some concurrency,
>> in case some other CPU modify this variable while panic() is running.
>> I find it very unlikely, hence I removed it - but if people consider
>> this copy needed, I can respin this patch and keep it, even providing a
>> comment about that, in order to be explict about its need.
> 
> Only two sites change crash_kexec_post_notifiers, in
> arch/powerpc/kernel/fadump.c and drivers/hv/hv_common.c.  Yes, it's
> very unlikely that this will be altered while panic() is running and
> the consequences will be slight anyway.
> 
> But formally, we shouldn't do this, especially in a -stable
> backportable patch.  So please, let's have the minimal bugfix for now
> and we can look at removing that local at a later time?
> 

Thanks Andrew, I agree with you! I just sent a V5 with the bugfix alone,
not changing this local/global variable behavior.

Cheers,


Guilherme