linux-kernel - Re: [PATCH] sched/debug: avoid executing show

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Date:   Wed, 3 Aug 2022 19:14:52 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Liu Song <liusong@...ux.alibaba.com>, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com,
        vschneid@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/debug: avoid executing show_state and causing rcu
 stall warning


* Paul E. McKenney <paulmck@...nel.org> wrote:

> There is an rcu_sysrq_start() and rcu_sysrq_end() to suppress this.  
> These are invoked by __handle_sysrq().  The value of 
> rcu_cpu_stall_suppress should be non-zero during the sysrq execution, and 
> this should prevent RCU CPU stall warnings from being printed.
> 
> That said, the code currently does not support overlapping calls to the 
> various functions that suppress RCU CPU stall warnings.  Except that the 
> only other use in current mainline is rcu_panic(), which never 
> unsuppresses.
> 
> So could you please check the value of rcu_cpu_stall_suppress? Just in 
> case some other form of suppression was added somewhere that I missed?

So instead of supressing the (justified!) RCU stall messages, I'd much 
rather we apply only the minimal locking necessary for this debug printout.

That should also solve the stall warnings as a side effect.

Thanks,

	Ingo