From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_MUTT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1BCBDC28CC0 for ; Wed, 29 May 2019 13:05:31 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E947320673 for ; Wed, 29 May 2019 13:05:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727033AbfE2NFa (ORCPT ); Wed, 29 May 2019 09:05:30 -0400 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:45626 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726613AbfE2NF3 (ORCPT ); Wed, 29 May 2019 09:05:29 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 4389080D; Wed, 29 May 2019 06:05:29 -0700 (PDT) Received: from fuggles.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 71F863F59C; Wed, 29 May 2019 06:05:26 -0700 (PDT) Date: Wed, 29 May 2019 14:05:21 +0100 From: Will Deacon To: Peter Zijlstra Cc: Young Xiao <92siuyang@gmail.com>, linux@armlinux.org.uk, mark.rutland@arm.com, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, x86@kernel.org, kan.liang@linux.intel.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, ravi.bangoria@linux.vnet.ibm.com, mpe@ellerman.id.au, acme@redhat.com, eranian@google.com, fweisbec@gmail.com, jolsa@redhat.com Subject: Re: [PATCH] perf: Fix oops when kthread execs user process Message-ID: <20190529130521.GA11023@fuggles.cambridge.arm.com> References: <1559046689-24091-1-git-send-email-92siuyang@gmail.com> <20190528140103.GT2623@hirez.programming.kicks-ass.net> <20190528153224.GE20758@fuggles.cambridge.arm.com> <20190528173228.GW2623@hirez.programming.kicks-ass.net> <20190529091733.GA4485@fuggles.cambridge.arm.com> <20190529101042.GN2623@hirez.programming.kicks-ass.net> <20190529102022.GC4485@fuggles.cambridge.arm.com> <20190529125557.GU2623@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190529125557.GU2623@hirez.programming.kicks-ass.net> User-Agent: Mutt/1.11.1+86 (6f28e57d73f2) () Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 29, 2019 at 02:55:57PM +0200, Peter Zijlstra wrote: > On Wed, May 29, 2019 at 11:20:22AM +0100, Will Deacon wrote: > > Anyway, you can add my ack to your patch, but I bet we can remove that mm > > check :D > > I've ended up with the below. Ravi, can you test if that does indeed > obsolete your PPC patch? > > --- > Subject: perf: Fix perf_sample_regs_user() > From: Peter Zijlstra > Date: Wed May 29 14:37:24 CEST 2019 > > perf_sample_regs_user() uses 'current->mm' to test for the presence of > userspace, but this is insufficient, consider use_mm(). > > A better test is: '!(current->flags & PF_KTHREAD)', exec() clears > PF_KTHREAD after it sets the new ->mm but before it drops to userspace > for the first time. > > Possibly obsoletes: bf05fc25f268 ("powerpc/perf: Fix oops when kthread execs user process") > > Reported-by: Ravi Bangoria > Reported-by: Young Xiao <92siuyang@gmail.com> > Cc: Ravi Bangoria > Cc: Naveen N. Rao > Cc: Michael Ellerman > Cc: Jiri Olsa > Cc: Frederic Weisbecker > Cc: Stephane Eranian > Cc: Arnaldo Carvalho de Melo > Acked-by: Will Deacon > Fixes: 4018994f3d87 ("perf: Add ability to attach user level registers dump to sample") > Signed-off-by: Peter Zijlstra (Intel) > --- > kernel/events/core.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -5923,7 +5923,7 @@ static void perf_sample_regs_user(struct > if (user_mode(regs)) { Hmm, so it just occurred to me that Mark's observation is that the regs can be junk in some cases. In which case, should we be checking for kthreads first? Will