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Date:   Mon, 28 Sep 2020 11:01:43 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Chengming Zhou <zhouchengming@bytedance.com>
Cc:     linux-kernel@vger.kernel.org, pmladek@suse.com,
        sergey.senozhatsky@gmail.com, rostedt@goodmis.org,
        mingo@redhat.com, juri.lelli@redhat.com,
        vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
        bsegall@google.com, mgorman@suse.de, songmuchun@bytedance.com
Subject: Re: [External] Re: [PATCH 2/2] sched: mark
 PRINTK_DEFERRED_CONTEXT_MASK in __schedule()
Message-ID: <20200928090143.GA2628@hirez.programming.kicks-ass.net>
References: <20200927161130.33172-1-zhouchengming@bytedance.com>
 <20200927161130.33172-2-zhouchengming@bytedance.com>
 <20200928073202.GA2611@hirez.programming.kicks-ass.net>
 <40ab934e-5b8b-735b-da65-3043efab9fdc@bytedance.com>
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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.