linux-kernel - Re: [PATCH v2 2/5] sched_ext: Manage the validity of scx_rq

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: <20241202095847.GK24400@noisy.programming.kicks-ass.net>
Date: Mon, 2 Dec 2024 10:58:47 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Changwoo Min <multics69@...il.com>
Cc: tj@...nel.org, void@...ifault.com, mingo@...hat.com,
	changwoo@...lia.com, kernel-dev@...lia.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/5] sched_ext: Manage the validity of scx_rq_clock

On Mon, Dec 02, 2024 at 01:38:46PM +0900, Changwoo Min wrote:
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 95e40895a519..ab8015c8cab4 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -789,6 +789,7 @@ static void update_rq_clock_task(struct rq *rq, s64 delta)
>  void update_rq_clock(struct rq *rq)
>  {
>  	s64 delta;
> +	u64 clock;
>  
>  	lockdep_assert_rq_held(rq);
>  
> @@ -800,11 +801,14 @@ void update_rq_clock(struct rq *rq)
>  		SCHED_WARN_ON(rq->clock_update_flags & RQCF_UPDATED);
>  	rq->clock_update_flags |= RQCF_UPDATED;
>  #endif
> +	clock = sched_clock_cpu(cpu_of(rq));
> +	scx_rq_clock_update(rq, clock);

This adds a write to a second cacheline for *everyone* always.

Please don't do that.