linux-kernel - Re: [External] Re: [PATCH 2/2] sched: mark PRINTK_DEFERRED_CONTEXT_MASK in _

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Date:   Mon, 28 Sep 2020 11:01:43 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Chengming Zhou <zhouchengming@...edance.com>
Cc:     linux-kernel@...r.kernel.org, pmladek@...e.com,
        sergey.senozhatsky@...il.com, rostedt@...dmis.org,
        mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        bsegall@...gle.com, mgorman@...e.de, songmuchun@...edance.com
Subject: Re: [External] Re: [PATCH 2/2] sched: mark
 PRINTK_DEFERRED_CONTEXT_MASK in __schedule()

On Mon, Sep 28, 2020 at 04:54:53PM +0800, Chengming Zhou wrote:
> 
> 在 2020/9/28 下午3:32, Peter Zijlstra 写道:
> > On Mon, Sep 28, 2020 at 12:11:30AM +0800, Chengming Zhou wrote:
> >> The WARN_ON/WARN_ON_ONCE with rq lock held in __schedule() should be
> >> deferred by marking the PRINTK_DEFERRED_CONTEXT_MASK, or will cause
> >> deadlock on rq lock in the printk path.
> > It also shouldn't happen in the first place, so who bloody cares.
> 
> Yes, but if our box deadlock just because a WARN_ON_ONCE, we have to
> reboot : (

You have to reboot anyway to get into the fixed kernel.

> So these WARN_ON_ONCE have BUG_ON effect ?  Or we should change to use
> BUG_ON ?

Or use a sane printk implementation, I never suffer this.