From: Valentin Schneider <valentin.schneider@arm.com>
To: Quentin Perret <qperret@google.com>,
Peter Zijlstra <peterz@infradead.org>
Cc: Kirill Tkhai <ktkhai@virtuozzo.com>,
linux-kernel@vger.kernel.org, aaron.lwe@gmail.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: Fri, 8 Nov 2019 11:47:44 +0000 [thread overview]
Message-ID: <07d30588-22e6-e098-b591-29c7cd3c8054@arm.com> (raw)
In-Reply-To: <20191108110212.GA204618@google.com>
On 08/11/2019 11:02, Quentin Perret wrote:
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index a14487462b6c..6b983214e00f 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -6746,10 +6746,18 @@ done: __maybe_unused;
>> return NULL;
>> }
>>
>> +static int balance_fair(struct rq *rq, struct task_struct *prev, struct rq_flags *rf)
>> +{
>> + if (rq->cfs.nr_running)
>> + return 1;
>> +
>> + return newidle_balance(rq, rf) != 0;
>
> And you can ignore the RETRY_TASK case here under the assumption that
> we must have tried to pull from RT/DL before ending up here ?
>
I think we can ignore RETRY_TASK because this happens before the picking loop,
so we'll observe any new DL/RT task that got enqueued while newidle released
the lock. This also means we can safely break the balance loop in
pick_next_task() when we get RETRY_TASK, because we've got something to pick
(some new RT/DL task). This wants a comment though, methinks.
Other than that I agree with Quentin, it's a much cleaner approach and I quite
like it.
> Thanks,
> Quentin
>
next prev parent reply other threads:[~2019-11-08 11:48 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
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 [this message]
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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