Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753144Ab3EXJVT (ORCPT ); Fri, 24 May 2013 05:21:19 -0400 Received: from 173-166-109-252-newengland.hfc.comcastbusiness.net ([173.166.109.252]:37687 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750869Ab3EXJVR (ORCPT ); Fri, 24 May 2013 05:21:17 -0400 Date: Fri, 24 May 2013 11:21:00 +0200 From: Peter Zijlstra To: Vince Weaver Cc: Al Viro , linux-kernel@vger.kernel.org, Paul Mackerras , Ingo Molnar , Arnaldo Carvalho de Melo , trinity@vger.kernel.org Subject: Re: OOPS in perf_mmap_close() Message-ID: <20130524092100.GI23650@twins.programming.kicks-ass.net> References: <20130523044803.GA25399@ZenIV.linux.org.uk> <20130523125218.GB23650@twins.programming.kicks-ass.net> <20130523152611.GE23650@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1648 Lines: 43 On Thu, May 23, 2013 at 07:40:12PM -0400, Vince Weaver wrote: > On Thu, 23 May 2013, Peter Zijlstra wrote: > > > On Thu, May 23, 2013 at 10:10:36AM -0400, Vince Weaver wrote: > > > > > > I can confirm your patch avoids the oops on my machine. > > > > > > It does lead to interesting behavior if I run the sample program > > > multiple times (with added printfs): > > > > > > vince@core2:~$ ./perf_mmap_close_bug > > > mmap1=0x7f06a6e90000 > > > mmap2=0x7f06a6e7f000 > > > vince@core2:~$ ./perf_mmap_close_bug > > > mmap1=0x7f878a138000 > > > mmap2=0x7f878a127000 > > > vince@core2:~$ ./perf_mmap_close_bug > > > mmap1=0xffffffffffffffff > > > Error opening fd2 Invalid argument > > > > > > and then it never successfully completes again. Is this unexpected > > > behavior? > > > > Sounds weird to me, I'll see if I can reproduce/understand. > > I tracked this down in case you haven't already. > > The problem is that in the kernel patched > with your patch locked_vm is getting decremented twice in the sample code > and going negative. I'm not sure why this isn't a problem until the > third time through. Here are my crude debug printk > results from kernel/events/core.c D'uh I think I see what's happening.. we haev split the mmap state between the ringbuffer and event objects and since we have two events and one ringbuffer we're hosed. Let me try and straighten this out. -- 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/