Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965114AbaD3VEe (ORCPT ); Wed, 30 Apr 2014 17:04:34 -0400 Received: from mail-qa0-f48.google.com ([209.85.216.48]:51001 "EHLO mail-qa0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751382AbaD3VEc (ORCPT ); Wed, 30 Apr 2014 17:04:32 -0400 X-Google-Original-From: Vince Weaver Date: Wed, 30 Apr 2014 17:08:00 -0400 (EDT) From: Vince Weaver To: Peter Zijlstra cc: Vince Weaver , Ingo Molnar , linux-kernel@vger.kernel.org, Thomas Gleixner , Steven Rostedt Subject: Re: [perf] more perf_fuzzer memory corruption In-Reply-To: <20140430184437.GH17778@laptop.programming.kicks-ass.net> Message-ID: References: <20140418165958.GQ13658@twins.programming.kicks-ass.net> <20140418171516.GR13658@twins.programming.kicks-ass.net> <20140429094632.GP27561@twins.programming.kicks-ass.net> <20140429190108.GB30445@twins.programming.kicks-ass.net> <20140430184437.GH17778@laptop.programming.kicks-ass.net> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 30 Apr 2014, Peter Zijlstra wrote: > > Vince, could you add the below to whatever tracing muck you already > have? > > After staring at your traces all day with Thomas, we have doubts about > the refcount integrity. I've been staring at traces all day too. Will try your patch tomorrow. >From my staring, what looks like is happening in the trace is: task_sched_in in parent adds our freed (but alive in child) event: perf_fuzzer-2517 [001] 215.228165: bprint: perf_swevent_add: VMW add_rcu: 0xffff880036cbb000 This adds the event to the swevent_hlist the child is in the process of exiting, eventually frees the event perf_fuzzer-3634 [006] 215.228250: function: perf_release perf_fuzzer-3634 [006] 215.228250: function: perf_event_release_kernel perf_fuzzer-3634 [006] 215.228251: function: perf_group_detach perf_fuzzer-3634 [006] 215.228251: function: perf_event__header_size perf_fuzzer-3634 [006] 215.228251: function: perf_remove_from_context Which then does list_del_event() event->state=PERF_EVENT_STATE_OFF; Soon after the parent does task_sched_out which gets to event_sched_out() which hits if (event->state != PERF_EVENT_STATE_ACTIVE) return; So it never hits the event->pmu->del(event, 0); We need to get the value off the hlist. This analysis is probably wrong though because if it's as simple as that above then I'm not sure why it isn't easier to hit the bug. Vince -- 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/