linux-kernel - Re: [PATCH v2] x86/nmi: Add an emergency handler in nmi_desc & use it in nmi_shootdown

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Message-ID: <e63226d5a0e3e2c942202972c099617aee999c1a.camel@surriel.com>
Date: Tue, 03 Dec 2024 20:00:02 -0500
From: Rik van Riel <riel@...riel.com>
To: Waiman Long <longman@...hat.com>, Thomas Gleixner <tglx@...utronix.de>, 
 Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen
 <dave.hansen@...ux.intel.com>,  Peter Zijlstra <peterz@...radead.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, "H. Peter Anvin"
 <hpa@...or.com>
Subject: Re: [PATCH v2] x86/nmi: Add an emergency handler in nmi_desc & use
 it in nmi_shootdown_cpus()

On Tue, 2024-12-03 at 10:07 -0500, Waiman Long wrote:
> 
> Another way to fix this problem while allowing panic() calls from
> NMI context is by adding a new emergency NMI handler to the nmi_desc
> structure and provide a new set_emergency_nmi_handler() helper to
> atomically set crash_nmi_callback() in any context. The new emergency
> handler will be invoked first before other handlers in the linked
> list. That will eliminate the need to take any lock and serve the
> panic
> in NMI use case.
> 
> Signed-off-by: Waiman Long <longman@...hat.com>

I've seen that panic come by a number of times, but
never came up with a good fix.

Your idea certainly looks like it should work, and
avoid all the issues along the way.

Acked-by: Rik van Riel <riel@...riel.com>

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