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Date:   Tue, 10 Oct 2023 09:59:28 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Chen Yu <yu.c.chen@intel.com>
Cc:     Ingo Molnar <mingo@redhat.com>, Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Phil Auld <pauld@redhat.com>,
        Biju Das <biju.das.jz@bp.renesas.com>,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        linux-kernel@vger.kernel.org, Tim Chen <tim.c.chen@intel.com>,
        Chen Yu <yu.chen.surf@gmail.com>
Subject: Re: [PATCH] sched/fair: Use printk_deferred instead of printk in
 pick_eevdf()
Message-ID: <20231010075928.GA377@noisy.programming.kicks-ass.net>
References: <20231010032541.339606-1-yu.c.chen@intel.com>
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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.

No.. I detest printk_deferred with a passion. This is effectively a WARN
and we don't do silly buggers for them either.