linux-kernel - Re: [PATCH] sched/fair: Use printk_deferred instead of printk in pick

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Message-ID: <ZSZ5QE/r6GD5mOEf@chenyu5-mobl2.ccr.corp.intel.com>
Date:   Wed, 11 Oct 2023 18:30:24 +0800
From:   Chen Yu <yu.c.chen@...el.com>
To:     Phil Auld <pauld@...hat.com>
CC:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Biju Das <biju.das.jz@...renesas.com>,
        "Marek Szyprowski" <m.szyprowski@...sung.com>,
        <linux-kernel@...r.kernel.org>, "Tim Chen" <tim.c.chen@...el.com>,
        Chen Yu <yu.chen.surf@...il.com>
Subject: Re: [PATCH] sched/fair: Use printk_deferred instead of printk in
 pick_eevdf()

On 2023-10-10 at 08:26:00 -0400, Phil Auld wrote:
> On Tue, Oct 10, 2023 at 09:59:28AM +0200 Peter Zijlstra wrote:
> > On Tue, Oct 10, 2023 at 11:25:41AM +0800, Chen Yu wrote:
> > > When no eligible entity is found in pick_eevdf(), it has to pick
> > > the entity with smallest vruntime. This indicates a potential issue
> > > and scheduler will print this error.
> > > 
> > > However this printk could introduce possible circular locking issue
> > > because when the code path reaches here with the rq lock held, the
> > > printk could trigger further scheduling which loops back to the
> > > scheduler.
> > > 
> > > Use printk_deferred() to defer the console write from current context
> > > to the irq work in the next tick.
> 
> Chen: I was not actually suggesting you make this change, just answering your
> question about printk/rq lock.  You don't need to put that line in there.
>

Phil,

Sorry for misunderstanding that, and thanks again for your guidance.

thanks,
Chenyu