Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753097AbZL3PIy (ORCPT ); Wed, 30 Dec 2009 10:08:54 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753078AbZL3PIw (ORCPT ); Wed, 30 Dec 2009 10:08:52 -0500 Received: from bombadil.infradead.org ([18.85.46.34]:45236 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753072AbZL3PIv (ORCPT ); Wed, 30 Dec 2009 10:08:51 -0500 Subject: Re: [PATCH 1/1] perf_event: add check for group_list if the parent isn't counted From: Peter Zijlstra To: Wang Liming Cc: Ingo Molnar , Frederic Weisbecker , Paul Mackerras , Thomas Gleixner , linux-kernel@vger.kernel.org In-Reply-To: <4B3B657B.2070009@windriver.com> References: <1262172487-13694-1-git-send-email-liming.wang@windriver.com> <1262176125.7135.207.camel@laptop> <4B3B657B.2070009@windriver.com> Content-Type: text/plain; charset="UTF-8" Date: Wed, 30 Dec 2009 16:08:04 +0100 Message-ID: <1262185684.7135.222.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2426 Lines: 74 On Wed, 2009-12-30 at 22:36 +0800, Wang Liming wrote: > > Best I can make of it is that there is a race where the parent gets his > > context instantiated and we manage to get the mutex before the other > > thread manages to add the first event. > > > > Then we observe parent_event_ctx but have an empty list. > > > > Is that it? > I didn't find this case. > In my case, if I perf record a existing process with "--pid" and finish record, > and if later the recorded process forks a process, the condition will occur. Ah, right, that will lead to the same state, since closing the last counter will not remove the context. Does the below also fix your issue? --- Subject: perf: Fix NULL deref in inheritance code From: Peter Zijlstra Date: Wed Dec 30 16:00:35 CET 2009 Liming found a NULL deref when a task has a perf context but no counters when it forks. This can occur in two cases, a race during construction where the fork hits after installing the context but before the first counter gets inserted, or more reproducably, a fork after the last counter is closed (which leaves the context around). CC: stable@kernel.org Reported-by: Wang Liming Signed-off-by: Peter Zijlstra --- kernel/perf_event.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) Index: linux-2.6/kernel/perf_event.c =================================================================== --- linux-2.6.orig/kernel/perf_event.c +++ linux-2.6/kernel/perf_event.c @@ -5149,7 +5149,7 @@ int perf_event_init_task(struct task_str GFP_KERNEL); if (!child_ctx) { ret = -ENOMEM; - goto exit; + break; } __perf_event_init_context(child_ctx, child); @@ -5165,7 +5165,7 @@ int perf_event_init_task(struct task_str } } - if (inherited_all) { + if (child_ctx && inherited_all) { /* * Mark the child context as a clone of the parent * context, or of whatever the parent is a clone of. @@ -5185,7 +5185,6 @@ int perf_event_init_task(struct task_str get_ctx(child_ctx->parent_ctx); } -exit: mutex_unlock(&parent_ctx->mutex); perf_unpin_context(parent_ctx); -- 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/