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Thu, 14 Nov 2024 13:58:02 -0500 X-MC-Unique: yRCtM6ANOz6aPkN5AEOm6Q-1 X-Mimecast-MFC-AGG-ID: yRCtM6ANOz6aPkN5AEOm6Q Received: from mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.15]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 4C61A1956096; Thu, 14 Nov 2024 18:58:01 +0000 (UTC) Received: from pauld.westford.csb (unknown [10.22.88.110]) by mx-prod-int-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 4CDD81956089; Thu, 14 Nov 2024 18:57:58 +0000 (UTC) Date: Thu, 14 Nov 2024 13:57:55 -0500 From: Phil Auld To: Jon Kohler Cc: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , linux-kernel@vger.kernel.org Subject: Re: [PATCH] sched: hoist ASSERT_EXCLUSIVE_WRITER(p->on_rq) above WRITE_ONCE Message-ID: <20241114185755.GG471026@pauld.westford.csb> References: <20241114165352.1824956-1-jon@nutanix.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20241114165352.1824956-1-jon@nutanix.com> X-Scanned-By: MIMEDefang 3.0 on 10.30.177.15 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 > --- > 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 Cheers, Phil --