linux-kernel - Re: [PATCH v2 04/15] sched/core: Fix picking of tasks for core scheduling with DL server

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Message-ID: <8567127c-c009-4960-a0e9-59f852571b11@redhat.com>
Date: Fri, 5 Apr 2024 11:37:30 +0200
From: Daniel Bristot de Oliveira <bristot@...hat.com>
To: "Joel Fernandes (Google)" <joel@...lfernandes.org>,
 linux-kernel@...r.kernel.org, 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>
Cc: Suleiman Souhlal <suleiman@...gle.com>,
 Youssef Esmat <youssefesmat@...gle.com>, David Vernet <void@...ifault.com>,
 Thomas Gleixner <tglx@...utronix.de>, "Paul E . McKenney"
 <paulmck@...nel.org>, joseph.salisbury@...onical.com,
 Luca Abeni <luca.abeni@...tannapisa.it>,
 Tommaso Cucinotta <tommaso.cucinotta@...tannapisa.it>,
 Vineeth Pillai <vineeth@...byteword.org>,
 Shuah Khan <skhan@...uxfoundation.org>, Phil Auld <pauld@...hat.com>
Subject: Re: [PATCH v2 04/15] sched/core: Fix picking of tasks for core
 scheduling with DL server

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