linux-kernel - Re: [PATCH] ARM64: smp: Silence suspicious RCU usage with ipi tracepoints

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Message-ID: <20150624210131.384d5505@gandalf.local.home>
Date:	Wed, 24 Jun 2015 21:01:31 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Stephen Boyd <sboyd@...eaurora.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	John Stultz <john.stultz@...aro.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Nicolas Pitre <nicolas.pitre@...aro.org>
Subject: Re: [PATCH] ARM64: smp: Silence suspicious RCU usage with ipi
 tracepoints

On Wed, 24 Jun 2015 23:29:30 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> On Wed, Jun 24, 2015 at 01:14:18PM -0700, Stephen Boyd wrote:
> > John Stultz reported an RCU splat on ARM with ipi trace events
> > enabled. It looks like the same problem exists on ARM64.
> > 
> > At this point in the IPI handling path we haven't called
> > irq_enter() yet, so RCU doesn't know that we're about to exit
> > idle and properly warns that we're using RCU from an idle CPU.
> > Use trace_ipi_entry_rcuidle() instead of trace_ipi_entry() so
> > that RCU is informed about our exit from idle.
> 
> I have a problem with $subject. It says 'silence', whereas afaict this
> fixes an actual bug, so it should be 'fixes'.

Agreed, otherwise Acked-by: Steven Rostedt <rostedt@...dmis.org>

-- Steve
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