linux-kernel - Re: [PATCH 00/12] perf: more fixes

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Message-ID: <20160311142346.GE6344@twins.programming.kicks-ass.net>
Date:	Fri, 11 Mar 2016 15:23:46 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vince Weaver <vince@...ter.net>
Cc:	mingo@...nel.org, alexander.shishkin@...ux.intel.com,
	eranian@...gle.com, linux-kernel@...r.kernel.org,
	dvyukov@...gle.com, andi@...stfloor.org, jolsa@...hat.com,
	panand@...hat.com, sasha.levin@...cle.com, oleg@...hat.com,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH 00/12] perf: more fixes

On Thu, Mar 10, 2016 at 09:44:30AM -0500, Vince Weaver wrote:
> On Thu, 10 Mar 2016, Peter Zijlstra wrote:
> 
> > On Wed, Feb 24, 2016 at 06:45:39PM +0100, Peter Zijlstra wrote:
> > 
> > Boris, who has been running syz-kaller on AMD hardware and was hitting a
> > very similar bug with the AMD-IBS code, says its not fixed it for him,
> > so maybe there's still more to find.
> 
> sorry I am not being much help with this big syz-kaller bug hunt, but I 
> just wanted to chime in that there's a (probably the same) long standing 
> IBS bug that perf_fuzzer hits all the time too, it was bad enough 
> that I had to stop running perf_fuzzer on my AMD box.

The below seems to fix the IBS issue tickled by syz-kaller on my
machine. I've not yet ran perf-fuzzer, which seems able to tickle a
different set of bugs.

---
Subject: perf, amb: Fix IBS throttle

When the IBS IRQ handler get a !0 return from perf_event_overflow;
meaning it should throttle the event, it only disables it, it doesn't
call perf_ibs_stop().

This confuses the state machine, as we'll use pmu::start() ->
perf_ibs_start() to unthrottle.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/events/amd/ibs.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/events/amd/ibs.c b/arch/x86/events/amd/ibs.c
index 51087c29b2c2..7956d29762ef 100644
--- a/arch/x86/events/amd/ibs.c
+++ b/arch/x86/events/amd/ibs.c
@@ -599,7 +599,7 @@ static int perf_ibs_handle_irq(struct perf_ibs *perf_ibs, struct pt_regs *iregs)
 	throttle = perf_event_overflow(event, &data, &regs);
 out:
 	if (throttle)
-		perf_ibs_disable_event(perf_ibs, hwc, *config);
+		perf_ibs_stop(event, 0);
 	else
 		perf_ibs_enable_event(perf_ibs, hwc, period >> 4);