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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aGZxFRVxHouLaMPg@tiehlicka>
Date: Thu, 3 Jul 2025 14:01:25 +0200
From: Michal Hocko <mhocko@...e.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: Chen Yu <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 03-07-25 13:50:06, Peter Zijlstra wrote:
> On Thu, Jul 03, 2025 at 11:28:46AM +0200, Michal Hocko wrote:
> 
> > But thinking about this some more, this would be racy same as the
> > PF_EXITING check. This is not my area but is this performance sensitive
> > path that couldn't live with the proper find_lock_task_mm?
> 
> find_lock_task_mm() seems eminently unsuitable for accounting --
> iterating the task group is insane.
> 
> Looking at this, the mm_struct lifetimes suck.. task_struct reference
> doesn't help, rcu doesn't help :-(
> 
> Also, whatever the solution it needs to be inside this count_memcg_*()
> nonsense, because nobody wants this overhead, esp. not for something
> daft like accounting.
> 
> My primary desire at this point is to just revert the patch that caused
> this. Accounting just isn't worth it. Esp. not since there is already a
> tracepoint in this path -- people that want to count crap can very well
> get their numbers from that.

I would tend to agree with this. Doing the accounting race free on a
remote task is nasty and if this is a rare event that could be avoided
then it should be just dropped than racy and oops prone.

-- 
Michal Hocko
SUSE Labs