linux-kernel - Re: [PATCH] sched/numa: Fix NULL pointer access to mm

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Message-ID: <20250703115504.GU1613200@noisy.programming.kicks-ass.net>
Date: Thu, 3 Jul 2025 13:55:04 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Michal Hocko <mhocko@...e.com>
Cc: "Chen, Yu C" <yu.c.chen@...el.com>, Ingo Molnar <mingo@...hat.com>,
	Juri Lelli <juri.lelli@...hat.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tim Chen <tim.c.chen@...el.com>, linux-kernel@...r.kernel.org,
	Jirka Hladky <jhladky@...hat.com>,
	Srikanth Aithal <Srikanth.Aithal@....com>,
	Suneeth D <Suneeth.D@....com>, Libo Chen <libo.chen@...cle.com>
Subject: Re: [PATCH] sched/numa: Fix NULL pointer access to mm_struct durng
 task swap

On Thu, Jul 03, 2025 at 01:51:23PM +0200, Michal Hocko wrote:
> Why not use find_lock_task_mm if task_lock is acceptable for this code
> path?

Having to take locks just to count a number nobody is ever going to look
at is silly. Iterating the whole thread group (might be hundreds or
thousands of tasks) just to maybe find one when racing with a fatal
signal is even more silly.