linux-kernel - Re: [RFT] sched_ext: Skip stack trace capture in NMI context

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Message-ID: <3662F4D2-C5ED-4C53-BF7C-B7B17047BFDB@nvidia.com>
Date: Wed, 24 Dec 2025 17:42:15 +0000
From: Joel Fernandes <joelagnelf@...dia.com>
To: Steven Rostedt <rostedt@...dmis.org>
CC: Tejun Heo <tj@...nel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, David Vernet <void@...ifault.com>, Andrea
 Righi <arighi@...dia.com>, Changwoo Min <changwoo@...lia.com>, Ingo Molnar
	<mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Juri Lelli
	<juri.lelli@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>, Ben Segall <bsegall@...gle.com>,
	Mel Gorman <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>,
	"sched-ext@...ts.linux.dev" <sched-ext@...ts.linux.dev>
Subject: Re: [RFT] sched_ext: Skip stack trace capture in NMI context



> On Dec 24, 2025, at 9:17 AM, Steven Rostedt <rostedt@...dmis.org> wrote:
> 
> On Tue, 23 Dec 2025 18:58:33 -0500
> Joel Fernandes <joelagnelf@...dia.com> wrote:
> 
>> Some documentation suggests IST is required for reliable NMI stack tracing
>> [1] [2] which 32-bit does not have.
>> ”If an interrupt or other exception is taken while the stack or other unwind
>> state is in an inconsistent state, it may not be possible to reliably unwind,
>> and it may not be possible to identify whether such unwinding will be
>> reliable. See below for examples.“
>> 
>> Probably the issue happens to be more of printing garbage than crashing the
>> kernel, but I am not convinced it is stable. Hmm.
> 
> Correct. It's about reliable stack traces, as live kernel patching requires
> that the stack it looks at is reliable before it can modify the code. What
> happens if it's not reliable, means it will just stop at the interrupt
> handler and you don't get to see the rest (or you'll see a bunch of
> functions with "?" in front of them).

Ah, thanks Steve for clarifying!

 - Joel


> 
> -- Steve