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=-5.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,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 4C55CC28CC0 for ; Wed, 29 May 2019 10:10:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 222E6208C3 for ; Wed, 29 May 2019 10:10:56 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="McFL6gJP" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726501AbfE2KKz (ORCPT ); Wed, 29 May 2019 06:10:55 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:37968 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726076AbfE2KKx (ORCPT ); Wed, 29 May 2019 06:10:53 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=In-Reply-To:Content-Type:MIME-Version :References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=95Oxk8yU+7lW8gyKo1/2OpFJ/n7OwlhaWfOSt2Jh2II=; b=McFL6gJP1i+wIeMgFZ59Fim5k IDvtMHIF5SfmGl1JMacxqRL2kGI/ky/ZVTBcnnEy/CQNZ2hAAONCEnX+fkx1ekitpHqEgNtef2Ly1 lUZgOdcJDtSaXcsG08P+kX5ymVDaVbuppat2lI9cTXVOUTE7Lh2BShA4KePoXw/lZUsMUeicU2s4R 0K7F0KAFRaGx60tJBrZwgVJ79szyvqAIz+0b1ytxjE9HIRBsjI1YU2NpwknMtpMjld/WuLEK4i1BY xD0HoaZ5pHWInHch+tAZQRI9AW7CFXKgR+XGI1DmHu2qqYWJmctPFFMqfNSyVzdzSzIZYwtOA37ur l0Rxt/jAg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1hVvXf-0008LP-VT; Wed, 29 May 2019 10:10:44 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 78560201A7E40; Wed, 29 May 2019 12:10:42 +0200 (CEST) Date: Wed, 29 May 2019 12:10:42 +0200 From: Peter Zijlstra To: Will Deacon 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 Subject: Re: [PATCH] perf: Fix oops when kthread execs user process Message-ID: <20190529101042.GN2623@hirez.programming.kicks-ass.net> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190529091733.GA4485@fuggles.cambridge.arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) 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 10:17:33AM +0100, Will Deacon wrote: > On Tue, May 28, 2019 at 07:32:28PM +0200, Peter Zijlstra wrote: > > 'funny' thing that, perf_sample_regs_user() seems to assume that > > anything with current->mm is in fact a user task, and that assumption is > > just plain wrong, consider use_mm(). > > Right, I suppose that was attempting to handle interrupt skid from the PMU > overflow? Nah, just a broken test to determine if there is userspace at all. It is mostly right, just not completely :-) > > So I'm thinking the right thing to do here is something like the below; > > umh should get PF_KTHREAD cleared when it passes exec(). And this should > > also fix the power splat I'm thinking. > > > > --- > > > > diff --git a/kernel/events/core.c b/kernel/events/core.c > > index abbd4b3b96c2..9929404b6eb9 100644 > > --- a/kernel/events/core.c > > +++ b/kernel/events/core.c > > @@ -5923,7 +5923,7 @@ static void perf_sample_regs_user(struct perf_regs *regs_user, > > if (user_mode(regs)) { > > regs_user->abi = perf_reg_abi(current); > > regs_user->regs = regs; > > - } else if (current->mm) { > > + } else if (!(current->flags & PF_KTHREAD) && current->mm) { > > perf_get_regs_user(regs_user, regs, regs_user_copy); > > Makes sense, but under which circumstances would we have a NULL mm here? Dunno; I'm paranoid, and also: mm/memcontrol.c: if (in_interrupt() || !current->mm || (current->flags & PF_KTHREAD)) mm/vmacache.c: return current->mm == mm && !(current->flags & PF_KTHREAD); 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=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,T_DKIMWL_WL_HIGH,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 EB62AC28CC2 for ; Wed, 29 May 2019 10:10:53 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id C52ED208C3 for ; Wed, 29 May 2019 10:10:53 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="Kq30hWx5" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C52ED208C3 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=HtS8XxW9ykmXEJDQw68I37/bpLsIzBVtNJ+iM+csNJw=; b=Kq30hWx5l8E3lA 9BdLJwDTM+tpOfmubvzcYvxT87BNDiH7yO+GXp3owFHm1dEB+2QhdyxLlRPVSPoimyFDfrIATTMI+ I3XBNgErp4+j9m4jepXc8JRyYNVSJQZOoZEGMQLjC3hY8LT0spSkBWLtAM+0MAw4tWAr1W/9l2EAZ 474qOlyeDyR+jfXC+71SgatJCBhIGAlSaydhzlTz2scNzEIAz7sCCxbefytlOrD1K1bsoBb6FiRUh 1V7oK6FJjeu4RL2eTEg6OaqCoe4vJ2yWeNuCrnRPYzKNqBtXzOKxkpd07C8E9puqdh3AhDduDcBBf Fwtj9afuDaQPC+EE3HeA==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1hVvXj-0008LY-FP; Wed, 29 May 2019 10:10:47 +0000 Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=hirez.programming.kicks-ass.net) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1hVvXf-0008LP-VT; Wed, 29 May 2019 10:10:44 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 78560201A7E40; Wed, 29 May 2019 12:10:42 +0200 (CEST) Date: Wed, 29 May 2019 12:10:42 +0200 From: Peter Zijlstra To: Will Deacon Subject: Re: [PATCH] perf: Fix oops when kthread execs user process Message-ID: <20190529101042.GN2623@hirez.programming.kicks-ass.net> 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> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190529091733.GA4485@fuggles.cambridge.arm.com> User-Agent: Mutt/1.10.1 (2018-07-13) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mark.rutland@arm.com, Young Xiao <92siuyang@gmail.com>, mpe@ellerman.id.au, x86@kernel.org, linux@armlinux.org.uk, linux-kernel@vger.kernel.org, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, ravi.bangoria@linux.vnet.ibm.com, linux-arm-kernel@lists.infradead.org, kan.liang@linux.intel.com Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Wed, May 29, 2019 at 10:17:33AM +0100, Will Deacon wrote: > On Tue, May 28, 2019 at 07:32:28PM +0200, Peter Zijlstra wrote: > > 'funny' thing that, perf_sample_regs_user() seems to assume that > > anything with current->mm is in fact a user task, and that assumption is > > just plain wrong, consider use_mm(). > > Right, I suppose that was attempting to handle interrupt skid from the PMU > overflow? Nah, just a broken test to determine if there is userspace at all. It is mostly right, just not completely :-) > > So I'm thinking the right thing to do here is something like the below; > > umh should get PF_KTHREAD cleared when it passes exec(). And this should > > also fix the power splat I'm thinking. > > > > --- > > > > diff --git a/kernel/events/core.c b/kernel/events/core.c > > index abbd4b3b96c2..9929404b6eb9 100644 > > --- a/kernel/events/core.c > > +++ b/kernel/events/core.c > > @@ -5923,7 +5923,7 @@ static void perf_sample_regs_user(struct perf_regs *regs_user, > > if (user_mode(regs)) { > > regs_user->abi = perf_reg_abi(current); > > regs_user->regs = regs; > > - } else if (current->mm) { > > + } else if (!(current->flags & PF_KTHREAD) && current->mm) { > > perf_get_regs_user(regs_user, regs, regs_user_copy); > > Makes sense, but under which circumstances would we have a NULL mm here? Dunno; I'm paranoid, and also: mm/memcontrol.c: if (in_interrupt() || !current->mm || (current->flags & PF_KTHREAD)) mm/vmacache.c: return current->mm == mm && !(current->flags & PF_KTHREAD); _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel