linux-kernel - Re: [PATCH] sched_ext: Fix missing unlock in consume_dispatch

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: <Zw7MpoDcKmX9mGlK@slm.duckdns.org>
Date: Tue, 15 Oct 2024 10:12:22 -1000
From: Tejun Heo <tj@...nel.org>
To: Zhang Qiao <zhangqiao22@...wei.com>
Cc: David Vernet <void@...ifault.com>, 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_ext: Fix missing unlock in consume_dispatch_q()

Hello,

On Tue, Oct 15, 2024 at 10:29:17PM +0800, Zhang Qiao wrote:
> When the function consume_dispatch_q() returns true, the dsq lock may
> remains held and is not unlocked.
> 
> Signed-off-by: Zhang Qiao <zhangqiao22@...wei.com>
> ---
>  kernel/sched/ext.c | 16 +++++++++-------
>  1 file changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
> index 410a4df8a121..4d80aa3de00e 100644
> --- a/kernel/sched/ext.c
> +++ b/kernel/sched/ext.c
> @@ -2377,7 +2377,8 @@ static inline bool consume_remote_task(struct rq *this_rq, struct task_struct *p
>  static bool consume_dispatch_q(struct rq *rq, struct scx_dispatch_q *dsq)
>  {
>  	struct task_struct *p;
> -retry:
> +	bool ret = false;
> +
>  	/*
>  	 * The caller can't expect to successfully consume a task if the task's
>  	 * addition to @dsq isn't guaranteed to be visible somehow. Test
> @@ -2394,19 +2395,20 @@ static bool consume_dispatch_q(struct rq *rq, struct scx_dispatch_q *dsq)
>  		if (rq == task_rq) {
>  			task_unlink_from_dsq(p, dsq);
>  			move_local_task_to_local_dsq(p, 0, dsq, rq);
> -			raw_spin_unlock(&dsq->lock);
> -			return true;
> +			ret = true;
> +			break;
>  		}
>  
>  		if (task_can_run_on_remote_rq(p, rq, false)) {
> -			if (likely(consume_remote_task(rq, p, dsq, task_rq)))
> -				return true;
> -			goto retry;
> +			if (likely(consume_remote_task(rq, p, dsq, task_rq))) {
> +				ret = true;
> +				break;
> +			}
>  		}
>  	}
>  
>  	raw_spin_unlock(&dsq->lock);
> -	return false;
> +	return ret;

Has this change been tested at all? There's quite a bit of lock dancing
happening in the remote consumption path because the task needs to get
hot-migrated to the local CPU - consume_remote_task() calls
unlink_dsq_and_lock_src_rq() which drops the DSQ lock among other things.

Thanks.

-- 
tejun