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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_MUTT autolearn=unavailable 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 B45A3C28CC0 for ; Wed, 29 May 2019 16:44:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8E23E23E29 for ; Wed, 29 May 2019 16:44:19 +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="opPA4eY5" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726984AbfE2QoS (ORCPT ); Wed, 29 May 2019 12:44:18 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:47596 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726062AbfE2QoS (ORCPT ); Wed, 29 May 2019 12:44:18 -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=sxzAs+3HnzYC9EoyXWpVI8ykljmz5DFHFWPIJsNygyQ=; b=opPA4eY5MGIVUeEnQjWc3VAJ/ 4oXlxib2TTPMoX4NSr7melN23eKj6rkoxnQGfN6bLUlJ185bd3ROanNSCEa9f3oCT4lHpf94pxEWV ISvHz2YaNLlTt6LLkY+yt7WQ5KlhFsAU6o76aU3PMhiLsNwdZ57JEgNB6YxzN5IyY41YQSOqm+lRI YW5k1rqgXLu8LSpCwKHeGb2q0JJi+0CJH9px60p4G+8Cc29Ep2boOiEcaoiFTtz2l3hm88Wi2jRyH N0y0NQSVEBJicGKx1lUK22DOUrEoOK10QfZplisFB6S48RHDIWlgurzwmzq9vwtzEeuQAJEi52l+E 7b7E2XGPw==; 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 1hW1gP-0002uk-4d; Wed, 29 May 2019 16:44:09 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 51939201D5AB3; Wed, 29 May 2019 18:44:07 +0200 (CEST) Date: Wed, 29 May 2019 18:44:07 +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, 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: <20190529164407.GA2623@hirez.programming.kicks-ass.net> References: <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> <20190529130521.GA11023@fuggles.cambridge.arm.com> <20190529132515.GW2623@hirez.programming.kicks-ass.net> <20190529143510.GA11154@fuggles.cambridge.arm.com> <20190529161955.GZ2623@hirez.programming.kicks-ass.net> <20190529162528.GB12420@fuggles.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190529162528.GB12420@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 05:25:28PM +0100, Will Deacon wrote: > > > > On Wed, May 29, 2019 at 02:05:21PM +0100, Will Deacon wrote: > > > > > On Wed, May 29, 2019 at 02:55:57PM +0200, Peter Zijlstra wrote: > > > > > > > > > > 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? > Sorry, I'm not trying to catch you out! Just trying to understand what the > semantics are supposed to be. > > I do find the concept of user_mode(regs) bizarre for the idle task. By the > above, we definitely have a bug on arm64 (user_mode(regs) tends to be > true for the idle task), and I couldn't figure out how you avoided it on > x86. I guess it happens to work because the stack is zero-initialised or > something? So lets take the whole thing: static void perf_sample_regs_user(struct perf_regs *regs_user, struct pt_regs *regs, struct pt_regs *regs_user_copy) { if (user_mode(regs)) { regs_user->abi = perf_reg_abi(current); regs_user->regs = regs; } else if (!(current->flags & PF_KTHREAD)) { perf_get_regs_user(regs_user, regs, regs_user_copy); } else { regs_user->abi = PERF_SAMPLE_REGS_ABI_NONE; regs_user->regs = NULL; } } This is called from the perf-generate-a-sample path, which is typically an exception (IRQ/NMI/whatever) or a software/tracepoint thing. In the exception case, the @regs argument are the exception register, as provided by your entry.S to your exception handlers. In the software/tracepoint thing, it is the result of perf_arch_fetch_caller_regs(). So @regs is always 'sane' and user_mode(regs) tells us if the exception came from userspace (and software/tracepoints always fail this, they 'obviously' don't come from userspace). If we're idle, we're not from userspace, so this branch doesn't matter. Next, we test if there is a userspace part _at_all_, this is the newly minted: '!(current->flags & PF_KTHREAD)', if that passes, we use architecture magic -- task_pt_regs() -- to get the user-regs. This can be crap. But since the idle task will always fail our test (as would the old one, idle->mm is always NULL), we'll never get here for idle. Then failing the above two, as we must for idle, we'll default to ABI_NONE/NULL. Does that help? 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=-2.5 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, T_DKIMWL_WL_HIGH,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 D43B6C28CC0 for ; Wed, 29 May 2019 16:44:15 +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 985BF23E29 for ; Wed, 29 May 2019 16:44:15 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="bOcAD2++" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 985BF23E29 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=Qbx+9magCJVcSs2ylxxD9F0rOksi0Clk3kWUwfImuYw=; b=bOcAD2++Q33QJj BR06ybNeniW3ikCE82bVda3MdHyRwV3I1fHgTJHU1z0wQ0ONgK3pCA13FGJ1D7uEhiUwltUj5IV8S KKkdIa5cXwYRF6Id70aj52Vabp5WXDxZJIA6ZwMsXLLuFOnKE26iLKf+BDHbWbS0b6+qWENkrAcmI kCIV8y5vtsY3CdoWNMPa1oY2iorOfy8Yc/i3up80v+NAF8xMqepEf5zgfgl6ZH4lnrH9YAeK+6NId DJIu1MLV8Do0IWDij3I2iiteV3VHDDIqiuH0aMTW9/RFthjuvowx+hdWL3XytfbvQrIpYzg3vXfbA LvmZeOX1xHdOLnQ3z5Ow==; 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 1hW1gS-0002ux-5E; Wed, 29 May 2019 16:44:12 +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 1hW1gP-0002uk-4d; Wed, 29 May 2019 16:44:09 +0000 Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 51939201D5AB3; Wed, 29 May 2019 18:44:07 +0200 (CEST) Date: Wed, 29 May 2019 18:44:07 +0200 From: Peter Zijlstra To: Will Deacon Subject: Re: [PATCH] perf: Fix oops when kthread execs user process Message-ID: <20190529164407.GA2623@hirez.programming.kicks-ass.net> References: <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> <20190529130521.GA11023@fuggles.cambridge.arm.com> <20190529132515.GW2623@hirez.programming.kicks-ass.net> <20190529143510.GA11154@fuggles.cambridge.arm.com> <20190529161955.GZ2623@hirez.programming.kicks-ass.net> <20190529162528.GB12420@fuggles.cambridge.arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190529162528.GB12420@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, jolsa@redhat.com, x86@kernel.org, linux@armlinux.org.uk, eranian@google.com, linux-kernel@vger.kernel.org, acme@redhat.com, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, ravi.bangoria@linux.vnet.ibm.com, fweisbec@gmail.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 05:25:28PM +0100, Will Deacon wrote: > > > > On Wed, May 29, 2019 at 02:05:21PM +0100, Will Deacon wrote: > > > > > On Wed, May 29, 2019 at 02:55:57PM +0200, Peter Zijlstra wrote: > > > > > > > > > > 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? > Sorry, I'm not trying to catch you out! Just trying to understand what the > semantics are supposed to be. > > I do find the concept of user_mode(regs) bizarre for the idle task. By the > above, we definitely have a bug on arm64 (user_mode(regs) tends to be > true for the idle task), and I couldn't figure out how you avoided it on > x86. I guess it happens to work because the stack is zero-initialised or > something? So lets take the whole thing: static void perf_sample_regs_user(struct perf_regs *regs_user, struct pt_regs *regs, struct pt_regs *regs_user_copy) { if (user_mode(regs)) { regs_user->abi = perf_reg_abi(current); regs_user->regs = regs; } else if (!(current->flags & PF_KTHREAD)) { perf_get_regs_user(regs_user, regs, regs_user_copy); } else { regs_user->abi = PERF_SAMPLE_REGS_ABI_NONE; regs_user->regs = NULL; } } This is called from the perf-generate-a-sample path, which is typically an exception (IRQ/NMI/whatever) or a software/tracepoint thing. In the exception case, the @regs argument are the exception register, as provided by your entry.S to your exception handlers. In the software/tracepoint thing, it is the result of perf_arch_fetch_caller_regs(). So @regs is always 'sane' and user_mode(regs) tells us if the exception came from userspace (and software/tracepoints always fail this, they 'obviously' don't come from userspace). If we're idle, we're not from userspace, so this branch doesn't matter. Next, we test if there is a userspace part _at_all_, this is the newly minted: '!(current->flags & PF_KTHREAD)', if that passes, we use architecture magic -- task_pt_regs() -- to get the user-regs. This can be crap. But since the idle task will always fail our test (as would the old one, idle->mm is always NULL), we'll never get here for idle. Then failing the above two, as we must for idle, we'll default to ABI_NONE/NULL. Does that help? _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel