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[130.111.218.23]) by smtp.gmail.com with ESMTPSA id 3sm274960qkd.84.2018.12.06.07.35.31 (version=TLS1_2 cipher=ECDHE-RSA-CHACHA20-POLY1305 bits=256/256); Thu, 06 Dec 2018 07:35:31 -0800 (PST) From: Vince Weaver X-Google-Original-From: Vince Weaver Date: Thu, 6 Dec 2018 10:35:28 -0500 (EST) X-X-Sender: vince@macbook-air To: Jiri Olsa cc: Vince Weaver , linux-kernel@vger.kernel.org, Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Alexander Shishkin , Namhyung Kim , Andi Kleen Subject: Re: perf: perf_fuzzer triggers GPF in perf_prepare_sample In-Reply-To: <20181205183326.GE3836@krava> Message-ID: References: <20181205124538.GA19343@krava> <20181205163838.GA3836@krava> <20181205183326.GE3836@krava> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 5 Dec 2018, Jiri Olsa wrote: > On Wed, Dec 05, 2018 at 12:11:19PM -0500, Vince Weaver wrote: > > On Wed, 5 Dec 2018, Jiri Olsa wrote: > > > > > On Wed, Dec 05, 2018 at 01:45:38PM +0100, Jiri Olsa wrote: > > > > On Tue, Dec 04, 2018 at 10:54:55AM -0500, Vince Weaver wrote: > > > > > Hello, > > > > > > > > > > I was able to trigger another oops with the perf_fuzzer with current git. > > > > > > > > > > This is 4.20-rc5 after the fix for the very similar oops I previously > > > > > reported got committed. > > > > > > > > > > It seems to be pointing to the same location in the source as > > > > > before, I guess maybe triggered a different way? > > > > > > > > nice.. yep, looks the same > > > > > > > > > > > > > > Unfortunately this crash is not easily reproducible like the last one was. > > > > > > > > will check > > > > > > what model are hitting this on? > > > > Haswell. 6/60/3. > > > > While I can't deterministically trigger this, the fuzzer usually hits it > > within an hour or two. Is there any debug or printk messages I can > > add that would help figure out what's going on? > > I can't see how we could end up with that config other than > some corruption.. the only way I see could be that we touch > cpu->events array without checking its active_mask bit > > but that does not explain why the crash happened in the same > place as before Maybe it is a corruption issue. I had applied my own debug patch that would dump some info if data->callchain was NULL. But my debug code didn't trigger this time because it looks like data->callchain was "1" rather than "0". [27764.840179] BUG: unable to handle kernel NULL pointer dereference at 0000000000000001 [27764.840179] PGD 0 P4D 0 [27764.840180] Oops: 0000 [#1] SMP PTI [27764.840180] CPU: 1 PID: 18687 Comm: perf_fuzzer Tainted: G W 4.20.0-rc5+ #125 [27764.840180] Hardware name: LENOVO 10AM000AUS/SHARKBAY, BIOS FBKT72AUS 01/26/2014 Vince