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Message-ID: <8567127c-c009-4960-a0e9-59f852571b11@redhat.com>
Date: Fri, 5 Apr 2024 11:37:30 +0200
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Subject: Re: [PATCH v2 04/15] sched/core: Fix picking of tasks for core
 scheduling with DL server
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To: "Joel Fernandes (Google)" <joel@joelfernandes.org>,
 linux-kernel@vger.kernel.org, Ingo Molnar <mingo@redhat.com>,
 Peter Zijlstra <peterz@infradead.org>, Juri Lelli <juri.lelli@redhat.com>,
 Vincent Guittot <vincent.guittot@linaro.org>,
 Dietmar Eggemann <dietmar.eggemann@arm.com>,
 Steven Rostedt <rostedt@goodmis.org>, Ben Segall <bsegall@google.com>,
 Mel Gorman <mgorman@suse.de>, Valentin Schneider <vschneid@redhat.com>
Cc: Suleiman Souhlal <suleiman@google.com>,
 Youssef Esmat <youssefesmat@google.com>, David Vernet <void@manifault.com>,
 Thomas Gleixner <tglx@linutronix.de>, "Paul E . McKenney"
 <paulmck@kernel.org>, joseph.salisbury@canonical.com,
 Luca Abeni <luca.abeni@santannapisa.it>,
 Tommaso Cucinotta <tommaso.cucinotta@santannapisa.it>,
 Vineeth Pillai <vineeth@bitbyteword.org>,
 Shuah Khan <skhan@linuxfoundation.org>, Phil Auld <pauld@redhat.com>
References: <20240313012451.1693807-1-joel@joelfernandes.org>
 <20240313012451.1693807-5-joel@joelfernandes.org>
From: Daniel Bristot de Oliveira <bristot@redhat.com>
In-Reply-To: <20240313012451.1693807-5-joel@joelfernandes.org>
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On 3/13/24 02:24, Joel Fernandes (Google) wrote:
> * Use simple CFS pick_task for DL pick_task
> 
>   DL server's pick_task calls CFS's pick_next_task_fair(), this is wrong
>   because core scheduling's pick_task only calls CFS's pick_task() for
>   evaluation / checking of the CFS task (comparing across CPUs), not for
>   actually affirmatively picking the next task. This causes RB tree corruption
>   issues in CFS that were found by syzbot.
> 
> * Make pick_task_fair clear DL server
> 
>   A DL task pick might set ->dl_server, but it is possible the task will
>   never run (say the other HT has a stop task). If the CFS task is picked
>   in the future directly (say without DL server), ->dl_server will be
>   set. So clear it in pick_task_fair().
> 
> This fixes the KASAN issue reported by syzbot in set_next_entity().

These two sched/core patches seem to make sense.... things are working with them.

But I am not an expert in the CORE_SCHED, so I am adding them on top of the dl
server series in the v6... it is easier for people to review them...

The only thing I did was to adjust the log to fit into the 75 char that
checkpatch warns...

Thoughts?

-- Daniel