linux-kernel - Re: [PATCH] sched: hoist ASSERT_EXCLUSIVE_WRITER(p->on_rq) above WRITE

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: Windows password security audit tool. GUI, reports in PDF.

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

Message-ID: <20241114185755.GG471026@pauld.westford.csb>
Date: Thu, 14 Nov 2024 13:57:55 -0500
From: Phil Auld <pauld@...hat.com>
To: Jon Kohler <jon@...anix.com>
Cc: 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>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Valentin Schneider <vschneid@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched: hoist ASSERT_EXCLUSIVE_WRITER(p->on_rq) above
 WRITE_ONCE

On Thu, Nov 14, 2024 at 09:53:52AM -0700 Jon Kohler wrote:
> In {activate|deactivate}_task(), hoist ASSERT_EXCLUSIVE_WRITER() to be
> above WRITE_ONCE(p->on_rq), which matches the ordering listed in the
> KCSAN documentation, kcsan-checks.h code comments, and the usage
> pattern we already have in __block_task().
> 
> Signed-off-by: Jon Kohler <jon@...anix.com>
> ---
>  kernel/sched/core.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index a1c353a62c56..80a04c36b495 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -2066,16 +2066,16 @@ void activate_task(struct rq *rq, struct task_struct *p, int flags)
>  
>  	enqueue_task(rq, p, flags);
>  
> -	WRITE_ONCE(p->on_rq, TASK_ON_RQ_QUEUED);
>  	ASSERT_EXCLUSIVE_WRITER(p->on_rq);
> +	WRITE_ONCE(p->on_rq, TASK_ON_RQ_QUEUED);
>  }
>  
>  void deactivate_task(struct rq *rq, struct task_struct *p, int flags)
>  {
>  	SCHED_WARN_ON(flags & DEQUEUE_SLEEP);
>  
> -	WRITE_ONCE(p->on_rq, TASK_ON_RQ_MIGRATING);
>  	ASSERT_EXCLUSIVE_WRITER(p->on_rq);
> +	WRITE_ONCE(p->on_rq, TASK_ON_RQ_MIGRATING);
>  
>  	/*
>  	 * Code explicitly relies on TASK_ON_RQ_MIGRATING begin set *before*
> -- 
> 2.43.0
> 
> 

This looks fine to me and it makes sense to have the assert before the
write.  A quick grep showed that this is by no means a universal pattern
at the moment.


Reviewed-by: Phil Auld <pauld@...hat.com>


Cheers,
Phil

--