From: Quentin Perret <qperret@google.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Kirill Tkhai <ktkhai@virtuozzo.com>,
linux-kernel@vger.kernel.org, aaron.lwe@gmail.com,
valentin.schneider@arm.com, mingo@kernel.org, pauld@redhat.com,
jdesfossez@digitalocean.com, naravamudan@digitalocean.com,
vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
juri.lelli@redhat.com, rostedt@goodmis.org, bsegall@google.com,
mgorman@suse.de, kernel-team@android.com, john.stultz@linaro.org
Subject: Re: NULL pointer dereference in pick_next_task_fair
Date: Thu, 7 Nov 2019 19:27:53 +0000 [thread overview]
Message-ID: <20191107192753.GA55494@google.com> (raw)
In-Reply-To: <20191107184356.GF4114@hirez.programming.kicks-ass.net>
On Thursday 07 Nov 2019 at 19:43:56 (+0100), Peter Zijlstra wrote:
> But you mean something like:
>
> for (class = prev->sched_class; class; class = class->next) {
> if (class->balance(rq, rf))
> break;
> }
>
> put_prev_task(rq, prev);
>
> for_each_class(class) {
> p = class->pick_next_task(rq);
> if (p)
> return p;
> }
>
> BUG();
>
> like?
Right, something like that, though what I had was basically doing the
pull from within the pick_next_task_*() functions directly, like we were
doing before. I'm now seeing how easy it is to get this wrong, and that
even good-looking code in this area can be broken in very subtle ways,
so I didn't feel comfortable refactoring again so close to rc7. If you
feel more confident, I'm more than happy to test a patch implemeting the
above :)
> I had convinced myself we didn't need that, but that DL to RT case is
> pesky and might require it after all.
Yep, I don't see a way to avoid iterating all classes to do the balance,
one way or another ...
Thanks,
Quentin
next prev parent reply other threads:[~2019-11-07 19:28 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-28 17:46 NULL pointer dereference in pick_next_task_fair Quentin Perret
2019-10-28 21:49 ` Peter Zijlstra
2019-10-29 11:34 ` Peter Zijlstra
2019-10-29 11:50 ` Quentin Perret
2019-10-30 22:50 ` Ram Muthiah
2019-10-31 1:33 ` Valentin Schneider
2019-10-31 10:54 ` Valentin Schneider
2019-10-31 14:24 ` Valentin Schneider
2019-10-31 22:15 ` Valentin Schneider
2019-11-06 12:05 ` Peter Zijlstra
2019-11-06 13:08 ` Peter Zijlstra
2019-11-06 15:04 ` Qais Yousef
2019-11-06 16:57 ` Peter Zijlstra
2019-11-06 17:26 ` Qais Yousef
2019-11-06 15:51 ` Kirill Tkhai
2019-11-06 16:54 ` Peter Zijlstra
2019-11-06 17:27 ` Peter Zijlstra
2019-11-07 8:36 ` Kirill Tkhai
2019-11-07 13:26 ` Peter Zijlstra
2019-11-07 15:12 ` Kirill Tkhai
2019-11-07 15:42 ` Peter Zijlstra
2019-11-07 15:53 ` Kirill Tkhai
2019-11-07 15:38 ` Quentin Perret
2019-11-07 18:43 ` Peter Zijlstra
2019-11-07 19:27 ` Quentin Perret [this message]
2019-11-07 19:31 ` Peter Zijlstra
2019-11-07 19:42 ` Quentin Perret
2019-11-07 19:29 ` Peter Zijlstra
2019-11-08 11:02 ` Quentin Perret
2019-11-08 11:47 ` Valentin Schneider
2019-11-08 11:58 ` Quentin Perret
2019-11-08 12:00 ` Peter Zijlstra
2019-11-08 12:15 ` Quentin Perret
2019-11-08 12:35 ` Peter Zijlstra
2019-11-08 12:24 ` Peter Zijlstra
2019-11-08 11:55 ` Peter Zijlstra
2019-11-08 12:52 ` Peter Zijlstra
2019-11-07 16:09 ` Qais Yousef
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