Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752658AbaAQOJb (ORCPT ); Fri, 17 Jan 2014 09:09:31 -0500 Received: from mx1.redhat.com ([209.132.183.28]:50990 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750971AbaAQOJ2 (ORCPT ); Fri, 17 Jan 2014 09:09:28 -0500 Date: Fri, 17 Jan 2014 12:09:21 -0200 From: Arnaldo Carvalho de Melo To: Stephane Eranian Cc: LKML , Peter Zijlstra , Ingo Molnar , David Ahern , Jiri Olsa Subject: Re: [BUG] perf stat: corrupts memory when using PMU cpumask Message-ID: <20140117140921.GB8801@infradead.org> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Url: http://acmel.wordpress.com User-Agent: Mutt/1.5.20 (2009-12-10) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Em Fri, Jan 17, 2014 at 10:00:20AM +0100, Stephane Eranian escreveu: > 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? The idea here was to reduce the boilerplate that tools need to do when they are done dealing with evlists, so evlist__delete would do what the kernel does to resources allocated to a thread when it exits without explicitely deallocating them: release them all. So it seems, from your analysis, that bugs were left that need to be hammered out so that this works as intended. Can you share your patch? > 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/