linux-kernel - Re: perf: perf_fuzzer crashes on Pentium 4 systems

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Message-ID: <20190407202055.GX1421@uranus.lan>
Date:   Sun, 7 Apr 2019 23:20:55 +0300
From:   Cyrill Gorcunov <gorcunov@...il.com>
To:     Vince Weaver <vincent.weaver@...ne.edu>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        linux-kernel@...r.kernel.org,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Namhyung Kim <namhyung@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jiri Olsa <jolsa@...hat.com>,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: perf: perf_fuzzer crashes on Pentium 4 systems

On Thu, Apr 04, 2019 at 11:20:38PM +0300, Cyrill Gorcunov wrote:
> > the machine still crashes after this, but not right away.
> 
> yes, exactly, if look into disasm code we will see that 0x158
> offset points to hwc from event. Vince, gimme some time, probably
> the weekend so I would dive into the perf code more deeply and
> will try to make some debugging patch for more precise tracking
> of events. The kernel you're running is the latest -tip?

Vince, could you please disable alias events and see if it change
anything, once you have time? Note once we've aliases disabled the
counter for cpu cycles get used for NMI watchdog so PERF_COUNT_HW_CPU_CYCLES
won't be available in "perf" tool itself, but I guess perf_fuzzer uses
direct kernel syscall.
---
 arch/x86/events/intel/p4.c |    2 ++
 1 file changed, 2 insertions(+)

Index: linux-tip.git/arch/x86/events/intel/p4.c
===================================================================
--- linux-tip.git.orig/arch/x86/events/intel/p4.c
+++ linux-tip.git/arch/x86/events/intel/p4.c
@@ -622,6 +622,8 @@ static u64 p4_get_alias_event(u64 config
 	u64 config_match;
 	int i;
 
+	return 0;
+
 	/*
 	 * Only event with special mark is allowed,
 	 * we're to be sure it didn't come as malformed