linux-kernel - Re: [PATCH v2] sched/fair: Fix fault in reweight

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Message-ID: <8ab3272f-38b3-b7e9-abab-72a03ec0c872@linaro.org>
Date:   Tue, 25 Jan 2022 10:59:15 -0800
From:   Tadeusz Struk <tadeusz.struk@...aro.org>
To:     Vincent Guittot <vincent.guittot@...aro.org>,
        Daniel Jordan <daniel.m.jordan@...cle.com>
Cc:     peterz@...radead.org, Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Zhang Qiao <zhangqiao22@...wei.com>, stable@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        syzbot+af7a719bc92395ee41b3@...kaller.appspotmail.com
Subject: Re: [PATCH v2] sched/fair: Fix fault in reweight_entity

On 1/25/22 10:30, Tadeusz Struk wrote:
> On 1/25/22 01:14, Vincent Guittot wrote:
>> Could we use :
>> set_load_weight(p, !(p->__state & TASK_NEW));
>> instead of
>> set_load_weight(p, true);
>> in set_user_nice and __setscheduler_params.
> 
> Wouldn't that require READ_ONCE() and rmb() after the read?

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 848eaa0efe0e..3d7ede06b971 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6921,7 +6921,7 @@ void set_user_nice(struct task_struct *p, long nice)
                 put_prev_task(rq, p);

         p->static_prio = NICE_TO_PRIO(nice);
-       set_load_weight(p, true);
+       set_load_weight(p, !(READ_ONCE(p->__state) & TASK_NEW));
         old_prio = p->prio;
         p->prio = effective_prio(p);

That works for me. I will send a new version soon.

-- 
Thanks,
Tadeusz