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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 00530C433EF for ; Mon, 6 Sep 2021 09:33:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D99FE60E76 for ; Mon, 6 Sep 2021 09:33:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241564AbhIFJe7 (ORCPT ); Mon, 6 Sep 2021 05:34:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50188 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241280AbhIFJem (ORCPT ); Mon, 6 Sep 2021 05:34:42 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [IPv6:2a0a:51c0:0:12e:550::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 212AEC061575 for ; Mon, 6 Sep 2021 02:33:38 -0700 (PDT) Date: Mon, 6 Sep 2021 11:33:34 +0200 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1630920815; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=UN1huiQ1hCCmYuOPeMLCSrlLHdNvwG3s1qb3USL0hnU=; b=NmdztmKghE1Bc7KRxENnbWZ5+bQN1wfyO1qXUlkqF2aRcXNFw3FlyiBpVPxImEKo6hNR9I XcRhUzWHoy3IGmzzc90/2vITqg9k07LHokAJl+sIuMnOaIVQDV+poqIzAcGJJiRneuDOWb A+vHInpZ7CpR8UjkZf/VZ3p8uM9+XNAzeO2LRXaoVWOrCMxl6ugR6jSPjHq2281aP1rF59 D6a3/7uYFvGC2hF20VTW0FAtvLZriCrDwzF07kF43GPaniwt1Cw/sq47pJ8VCrL4BpWJib Tf8IxM9rp4FHRkNrwMLDntjXXLj+JlzojTToeQ0pXpHUKReXnw7LPCVxI6/h6g== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1630920815; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=UN1huiQ1hCCmYuOPeMLCSrlLHdNvwG3s1qb3USL0hnU=; b=Wtl0CVvFxyDBnW2zgKcdFd+qeMNsMwwW0Gv8NaE7McbXKMi04mfOJDPJV2+sANa3iTilJN MBL3uusm/38FEnBQ== From: Sebastian Andrzej Siewior To: Marco Elver Cc: Shuah Khan , tj@kernel.org, jiangshanlai@gmail.com, akpm@linux-foundation.org, andreyknvl@gmail.com, dvyukov@google.com, walter-zh.wu@mediatek.com, linux-kernel@vger.kernel.org, Thomas Gleixner Subject: Re: [PATCH v2] workqueue: Don't record workqueue stack holding raw_spin_lock Message-ID: <20210906093334.i7angdb7bda74puf@linutronix.de> References: <20210902200134.25603-1-skhan@linuxfoundation.org> <2bd3759d-cd13-24f5-2cbd-00505d98e0c9@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021-09-06 09:12:58 [+0200], Marco Elver wrote: > On Thu, Sep 02, 2021 at 05:46PM -0600, Shuah Khan wrote: > [...] > > > 3. Try to not allocate memory in stackdepot. Not sure this is feasible > > > without telling stackdepot to preallocate the max slabs on boot if RT. > > > > > > > We could. I have to ask though how much of the real world cases do we > > need to impact for the debug code to work? > > > > > Anything else? Because I don't think any of the options are satisfying. > > > > One option to consider is checking dry-run invalid nesting check and > > bail out if it is true in kasan_record_aux_stack() > > Sadly, if lockdep is off, this won't work. And we need a way to > generically fix this, as otherwise we still have a bug (which may also > cause issues on RT kernels). > > I propose we properly fix this and prevent stackdepot from replenishing > its "stack slab" pool if memory allocations cannot be done in the > current context. Specifically, I noticed technically it's a bug to use > either GFP_ATOMIC nor GFP_NOWAIT in certain non-preemptive contexts, > including raw_spin_locks (see gfp.h and ab00db216c9c7). I would say so, too. It is unlikely that we manage to remove raw_spin_lock_t from the workqueue code or that memory allocation with disabled preemption/ interrupts would be allowed on RT. Also as Marco pointed out, avoiding this code once a debug switch has been noticed is not good. > This is what kasan_record_aux_stack() via stackdepot does, and it's a > bug here regardless if lockdep is on or off. > > I've prepared a series (see attached draft patches) that allows telling > stackdepot to not replenish its pool if alloc_pages() cannot be called > at all (where GFP_ATOMIC/NOWAIT doesn't even work). This sounds good. debug_object has also a memory pool which is replenished from time to time. > The only downside is that saving a stack trace may fail if: stackdepot > runs out of space AND the same stack trace has not been recorded before. > I expect this to be unlikely, and a simple experiment (boot the kernel) > didn't result in any failure to record stack trace from insert_work(). > > I think this is a reasonable trade-off. And considering that we're > unsure if queuing work can or cannot be done from within an outer > raw_spin_lock'ed critical section, I don't see a better way. > > If you agree, I'll send this series out for further review. > > Thanks, > -- Marco Sebastian