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

Started byPeter Zijlstra <peterz@infradead.org>
First post2015-06-24 23:30 +0200
Last post2015-06-25 03:10 +0200
Articles 3 — 3 participants

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  Re: [PATCH] ARM64: smp: Silence suspicious RCU usage with ipi  tracepoints Peter Zijlstra <peterz@infradead.org> - 2015-06-24 23:30 +0200
    Re: [PATCH] ARM64: smp: Silence suspicious RCU usage with ipi tracepoints Stephen Boyd <sboyd@codeaurora.org> - 2015-06-25 00:10 +0200
    Re: [PATCH] ARM64: smp: Silence suspicious RCU usage with ipi  tracepoints Steven Rostedt <rostedt@goodmis.org> - 2015-06-25 03:10 +0200

#1171683 — Re: [PATCH] ARM64: smp: Silence suspicious RCU usage with ipi tracepoints

FromPeter Zijlstra <peterz@infradead.org>
Date2015-06-24 23:30 +0200
SubjectRe: [PATCH] ARM64: smp: Silence suspicious RCU usage with ipi tracepoints
Message-ID<pF0p4-4YX-7@gated-at.bofh.it>
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'.
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#1171702 — Re: [PATCH] ARM64: smp: Silence suspicious RCU usage with ipi tracepoints

FromStephen Boyd <sboyd@codeaurora.org>
Date2015-06-25 00:10 +0200
SubjectRe: [PATCH] ARM64: smp: Silence suspicious RCU usage with ipi tracepoints
Message-ID<pF11M-5Zy-3@gated-at.bofh.it>
In reply to#1171683
On 06/24/2015 02:29 PM, Peter Zijlstra 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'.

Fair enough. I can resend or whoever applies this patch can
s/Silence/Fix/ on the $subject.

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project

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#1171793

FromSteven Rostedt <rostedt@goodmis.org>
Date2015-06-25 03:10 +0200
Message-ID<pF3PX-1xZ-7@gated-at.bofh.it>
In reply to#1171683
On Wed, 24 Jun 2015 23:29:30 +0200
Peter Zijlstra <peterz@infradead.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@goodmis.org>

-- Steve
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