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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1B28EC433F5 for ; Fri, 22 Oct 2021 16:57:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DE4F1611CB for ; Fri, 22 Oct 2021 16:57:54 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233590AbhJVRAI (ORCPT ); Fri, 22 Oct 2021 13:00:08 -0400 Received: from foss.arm.com ([217.140.110.172]:56718 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233413AbhJVRAF (ORCPT ); Fri, 22 Oct 2021 13:00:05 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 7C5501063; Fri, 22 Oct 2021 09:57:47 -0700 (PDT) Received: from C02TD0UTHF1T.local (unknown [10.57.73.6]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id F252E3F73D; Fri, 22 Oct 2021 09:57:43 -0700 (PDT) Date: Fri, 22 Oct 2021 17:57:41 +0100 From: Mark Rutland To: Peter Zijlstra Cc: Kees Cook , x86@kernel.org, linux-kernel@vger.kernel.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, akpm@linux-foundation.org, zhengqi.arch@bytedance.com, linux@armlinux.org.uk, catalin.marinas@arm.com, will@kernel.org, mpe@ellerman.id.au, paul.walmsley@sifive.com, palmer@dabbelt.com, hca@linux.ibm.com, gor@linux.ibm.com, borntraeger@de.ibm.com, linux-arch@vger.kernel.org, ardb@kernel.org Subject: Re: [PATCH 2/7] stacktrace,sched: Make stack_trace_save_tsk() more robust Message-ID: <20211022165741.GG86184@C02TD0UTHF1T.local> References: <20211022150933.883959987@infradead.org> <20211022152104.215612498@infradead.org> <202110220919.46F58199D@keescook> <20211022164514.GE174703@worktop.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211022164514.GE174703@worktop.programming.kicks-ass.net> Precedence: bulk List-ID: X-Mailing-List: linux-arch@vger.kernel.org On Fri, Oct 22, 2021 at 06:45:14PM +0200, Peter Zijlstra wrote: > On Fri, Oct 22, 2021 at 09:25:02AM -0700, Kees Cook wrote: > > On Fri, Oct 22, 2021 at 05:09:35PM +0200, Peter Zijlstra wrote: > > > /** > > > * stack_trace_save_tsk - Save a task stack trace into a storage array > > > * @task: The task to examine > > > @@ -135,7 +142,6 @@ EXPORT_SYMBOL_GPL(stack_trace_save); > > > unsigned int stack_trace_save_tsk(struct task_struct *tsk, unsigned long *store, > > > unsigned int size, unsigned int skipnr) > > > { > > > - stack_trace_consume_fn consume_entry = stack_trace_consume_entry_nosched; > > > struct stacktrace_cookie c = { > > > .store = store, > > > .size = size, > > > @@ -143,11 +149,8 @@ unsigned int stack_trace_save_tsk(struct > > > .skip = skipnr + (current == tsk), > > > }; > > > > > > - if (!try_get_task_stack(tsk)) > > > - return 0; > > > + task_try_func(tsk, try_arch_stack_walk_tsk, &c); > > > > Pardon my thin understanding of the scheduler, but I assume this change > > doesn't mean stack_trace_save_tsk() stops working for "current", right? > > In trying to answer this for myself, I couldn't convince myself what value > > current->__state have here. Is it one of TASK_(UN)INTERRUPTIBLE ? > > current really shouldn't be using stack_trace_save_tsk(), and no you're > quite right, it will not work for current, irrespective of ->__state, > current will always be ->on_rq. Heh, we raced to say the same thing. :) > I started auditing stack_trace_save_tsk() users a few days ago, but > didn't look for this particular issue. I suppose I'll have to start over > with that. FWIW, this shape of thing was one of the reasons I wanted to split arch_stack_walk() into separate: * arch_stack_walk_current() * arch_stack_walk_current_regs() * arch_stack_walk_blocked_task() ... with similar applying here, since otherwise people won't consider the distinction between current / !current at the caller level, leading to junk like this. Thanks, Mark.