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

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Message-ID: <20150512132004.GL6776@linux.vnet.ibm.com>
Date:	Tue, 12 May 2015 06:20:04 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Chris Metcalf <cmetcalf@...hip.com>,
	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>,
	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 Tue, May 12, 2015 at 11:38:58AM +0200, Peter Zijlstra wrote:
> 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?

Agreed, a bit more debug state would be helpful.

							Thanx, Paul

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