Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752182AbaAQJA3 (ORCPT ); Fri, 17 Jan 2014 04:00:29 -0500 Received: from mail-oa0-f48.google.com ([209.85.219.48]:41832 "EHLO mail-oa0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751331AbaAQJAW (ORCPT ); Fri, 17 Jan 2014 04:00:22 -0500 MIME-Version: 1.0 Date: Fri, 17 Jan 2014 10:00:20 +0100 Message-ID: Subject: [BUG] perf stat: corrupts memory when using PMU cpumask From: Stephane Eranian To: Arnaldo Carvalho de Melo Cc: LKML , Peter Zijlstra , Ingo Molnar , David Ahern , Jiri Olsa Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, I have been debugging a NULL pointer issue with perf stat unit/scale code and in the process I ran into what appeared like a double-free issue reported by glibc. It took me a while to realize that it was because of memory corruption caused by a recent change in how evsel are freed. My test case is simple. I used RAPL but I think any event with a suggested cpumask in /sys/devices/XXX/cpumask will do: # perf stat -a -e power/energy-cores/ ls The issue boils down to the fact that evsels have their file descriptors closed twice nowadays. Once in __run_per_stat() via perf_evsel__close_fd() and twice in perf_evlist__close(). Now, calling close() twice is okay. However the fd is then set to -1. That's still okay with close(). The problem is elsewhere. It comes from the ncpus argument passed to perf_evsel__close(). It is DIFFERENT between the evsel and the evlist when cpumask are used. Take my case, 8 CPUs machine but a 1 CPU cpumask. The evsel allocates the xyarray for 1 CPU 1 thread. The fd are first close with 1 CPU, 1 thread. But then evlist_close() comes in and STILL thinks the events were using 8 CPUs, 1 thread and thus a xyarray of that size. And this causes writes to entries that are beyond the xyarray when the fds are set to -1, thereby causing memory corruption which I was lucky to catch via glibc. First, why are we closing the descriptors twice? Second, I have a fix that seems to work for me. It uses the evsel->cpus if evsel->cpus exists, otherwise it defaults to evtlist->cpus. Looks like a reasonable thing to do to me, but is it? I would rather avoid the double close altogether. Opinion? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/