Re: [PATCH] sched/debug: avoid executing show_state and causing rcu stall warning

From: Ingo Molnar <mingo@kernel.org>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Steven Rostedt <rostedt@goodmis.org>,
	Liu Song <liusong@linux.alibaba.com>,
	mingo@redhat.com, peterz@infradead.org, juri.lelli@redhat.com,
	vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
	bsegall@google.com, mgorman@suse.de, bristot@redhat.com,
	vschneid@redhat.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] sched/debug: avoid executing show_state and causing rcu stall warning
Date: Wed, 3 Aug 2022 19:14:52 +0200	[thread overview]
Message-ID: <YuqtDA4NY/8Z22aK@gmail.com> (raw)
In-Reply-To: <20220803140653.GD2125313@paulmck-ThinkPad-P17-Gen-1>

* Paul E. McKenney <paulmck@kernel.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