linux-kernel - Re: [PATCH 5/6] nohz: support PR_DATAPLANE

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Message-ID: <20150512093858.GI21418@twins.programming.kicks-ass.net>
Date:	Tue, 12 May 2015 11:38:58 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Chris Metcalf <cmetcalf@...hip.com>
Cc:	Gilad Ben Yossef <giladb@...hip.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>, Tejun Heo <tj@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	linux-doc@...r.kernel.org, linux-api@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/6] nohz: support PR_DATAPLANE_STRICT mode

On Fri, May 08, 2015 at 01:58:46PM -0400, Chris Metcalf wrote:
> +++ b/kernel/time/tick-sched.c
> @@ -436,6 +436,20 @@ static void dataplane_quiesce(void)
>  			(jiffies - start));
>  		dump_stack();
>  	}
> +
> +	/*
> +	 * Kill the process if it violates STRICT mode.  Note that this
> +	 * code also results in killing the task if a kernel bug causes an
> +	 * irq to be delivered to this core.
> +	 */
> +	if ((task->dataplane_flags & (PR_DATAPLANE_STRICT|PR_DATAPLANE_PRCTL))
> +	    == PR_DATAPLANE_STRICT) {
> +		pr_warn("Dataplane STRICT mode violated; process killed.\n");
> +		dump_stack();
> +		task->dataplane_flags &= ~PR_DATAPLANE_QUIESCE;
> +		local_irq_enable();
> +		do_group_exit(SIGKILL);
> +	}
>  }

So while I'm all for hard fails like this, can we not provide a wee bit
more information in the siginfo ? And maybe use a slightly less fatal
signal, such that userspace can actually catch it and dump state in
debug modes?
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