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=-12.9 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1, USER_IN_DEF_DKIM_WL 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 50B3CC4742C for ; Fri, 13 Nov 2020 11:09:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D756F20797 for ; Fri, 13 Nov 2020 11:08:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="fBXair5q" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726531AbgKMLI6 (ORCPT ); Fri, 13 Nov 2020 06:08:58 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54024 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726698AbgKMLGi (ORCPT ); Fri, 13 Nov 2020 06:06:38 -0500 Received: from mail-wm1-x342.google.com (mail-wm1-x342.google.com [IPv6:2a00:1450:4864:20::342]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6A2BAC0617A6 for ; Fri, 13 Nov 2020 03:06:13 -0800 (PST) Received: by mail-wm1-x342.google.com with SMTP id h62so8003065wme.3 for ; Fri, 13 Nov 2020 03:06:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=dA+kEQkhcLw+SoSuv0AIeD6qXLVmu5Sr7MknI9qkwoU=; b=fBXair5qjaak/59JdSXgS3XyyB9Zl4ewbvvrIAjDgFpB7I/6pMqmaGrdNIv9VuXSP2 t6anVkIisIxH8x5y4EWmdKuIv2LFTHS9bIFhVX8pbvzcgmNj9x8PEneUV8Zfwyg79ri7 9asViKIM2lGNqYalvQW52tBo6dxMPNIP/D1IrlFp+YKiw5Z1HPdnMvQpMpdQX1+hVqLF UkbZ29cb3K/Rj0Kb4oXydELXYoNeC5p0LWuR5FXdhbG6PvO4cAYUGQGo/58QfzBWPtek tShRUwS/ZZSKNBEyWtxLVfi5lff18kIoBJvWYdgSFVhkjdMNYXEfn8mXiw3xAtptJRUv chbg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=dA+kEQkhcLw+SoSuv0AIeD6qXLVmu5Sr7MknI9qkwoU=; b=qad4Tf9Z7auLyKOoFb8gRqVvsdtADVMzebtxwCzZQWkkB4v6zoXUV6h4GASj5VJ1B6 qqrDcG2b+qLPa9LQLCU6PJH+Ck0br9fOgURofMO5EvkQjXHTQmkrpdGZk2svYLb0qdsN Hqntf9YgAT9go4YiAqXX1lr7fXuoVa8PPAZ7AtLpLKFlselVkS3KRR8qCoG8QUuMIRgc lJDWa9py9p3AfHzgJRTNyrr8o8Uy2RJgEVYkMol9YZ3VlJF2nlKW/OBLDqULuxk++lJ9 XnPUClU638PNV2coyr6/6j8s49X0ZNgtA0u6Qwp9Tf1t+RW13WpdmiodXqvjluI/1QII HZ6w== X-Gm-Message-State: AOAM532VP1hm/GBggHrPAFN4yHA/gW4SYhhybHQDnBZOqxCYXtMbzyTj D1EhmU2iK5sZNbEvYm3sXgWJUQ== X-Google-Smtp-Source: ABdhPJztJ4Ckp3dVocLxWTwBzemEfZ1dSAquPhAEDSr5IcKTu4p/hOgv9SVr3y1hrv1ybxnPmYgPIQ== X-Received: by 2002:a1c:9916:: with SMTP id b22mr2042128wme.105.1605265571824; Fri, 13 Nov 2020 03:06:11 -0800 (PST) Received: from elver.google.com ([2a00:79e0:15:13:f693:9fff:fef4:2449]) by smtp.gmail.com with ESMTPSA id q12sm10935062wmc.45.2020.11.13.03.06.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 13 Nov 2020 03:06:10 -0800 (PST) Date: Fri, 13 Nov 2020 12:06:04 +0100 From: Marco Elver To: "Paul E. McKenney" Cc: Steven Rostedt , Anders Roxell , Andrew Morton , Alexander Potapenko , Dmitry Vyukov , Jann Horn , Mark Rutland , Linux Kernel Mailing List , Linux-MM , kasan-dev , rcu@vger.kernel.org, Peter Zijlstra , joel@joelfernandes.org Subject: Re: [PATCH] kfence: Avoid stalling work queue task without allocations Message-ID: <20201113110604.GA1907210@elver.google.com> References: <20201111182333.GA3249@paulmck-ThinkPad-P72> <20201111183430.GN517454@elver.google.com> <20201111192123.GB3249@paulmck-ThinkPad-P72> <20201111202153.GT517454@elver.google.com> <20201112001129.GD3249@paulmck-ThinkPad-P72> <20201112161439.GA2989297@elver.google.com> <20201112175406.GF3249@paulmck-ThinkPad-P72> <20201112181254.GA3113918@elver.google.com> <20201112200025.GG3249@paulmck-ThinkPad-P72> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201112200025.GG3249@paulmck-ThinkPad-P72> User-Agent: Mutt/1.14.6 (2020-07-11) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 12, 2020 at 12:00PM -0800, Paul E. McKenney wrote: > On Thu, Nov 12, 2020 at 07:12:54PM +0100, Marco Elver wrote: > > On Thu, Nov 12, 2020 at 09:54AM -0800, Paul E. McKenney wrote: > > > On Thu, Nov 12, 2020 at 05:14:39PM +0100, Marco Elver wrote: > > > > On Thu, Nov 12, 2020 at 01:49PM +0100, Marco Elver wrote: > > > > > On Thu, 12 Nov 2020 at 01:11, Paul E. McKenney wrote: > > > > [...] > > > > > > > This assert didn't fire yet, I just get more of the below. I'll keep > > > > > > > rerunning, but am not too hopeful... > > > > > > > > > > > > Is bisection a possibility? > > > > > > > > > > I've been running a bisection for past ~12h, and am making slow > > > > > progress. It might be another 12h, but I think it'll get there. > > > > > > > > Bisection gave me this: > > > > > > > > | git bisect start > > > > | # bad: [c07b306d7fa5680777e2132662d2e6c19fb53579] kfence: Avoid stalling work queue task without allocations > > > > | git bisect bad c07b306d7fa5680777e2132662d2e6c19fb53579 > > > > | # good: [3cea11cd5e3b00d91caf0b4730194039b45c5891] Linux 5.10-rc2 > > > > | git bisect good 27598e7e73260ed0b2917eb02d4a515ebb578313 > > > > | # good: [3e5acbea719e66ef3be64fe74c99cc905ca697dc] Merge remote-tracking branch 'wireless-drivers-next/master' into master > > > > | git bisect good 3e5acbea719e66ef3be64fe74c99cc905ca697dc > > > > | # good: [491a5a9a2fea28353d99621b8abb83b6928b4e36] Merge remote-tracking branch 'sound-asoc/for-next' into master > > > > | git bisect good 491a5a9a2fea28353d99621b8abb83b6928b4e36 > > > > | # bad: [502f8643d6e21c7e370a0b75131130cc51609055] Merge remote-tracking branch 'phy-next/next' into master > > > > | git bisect bad 502f8643d6e21c7e370a0b75131130cc51609055 > > > > | # good: [6693cb1fa5ea7b91ec00f9404776a095713face5] Merge remote-tracking branch 'tip/auto-latest' into master > > > > | git bisect good 6693cb1fa5ea7b91ec00f9404776a095713face5 > > > > | # bad: [b790e3afead9357195b6d1e1b6cd9b3521503ad2] Merge branch 'tglx-pc.2020.10.30a' into HEAD > > > > | git bisect bad b790e3afead9357195b6d1e1b6cd9b3521503ad2 > > > > | # bad: [765b512bb3d639bfad7dd43c288ee085236c7267] Merge branches 'cpuinfo.2020.11.06a', 'doc.2020.11.06a', 'fixes.2020.11.02a', 'lockdep.2020.11.02a', 'tasks.2020.11.06a' and 'torture.2020.11.06a' into HEAD > > > > | git bisect bad 765b512bb3d639bfad7dd43c288ee085236c7267 > > > > | # good: [01f9e708d9eae6335ae9ff25ab09893c20727a55] tools/rcutorture: Fix BUG parsing of console.log > > > > > > So torture.2020.11.06a is OK. > > > > > > > | git bisect good 01f9e708d9eae6335ae9ff25ab09893c20727a55 > > > > | # good: [1be6ab91e2db157faedb7f16ab0636a80745a073] srcu: Take early exit on memory-allocation failure > > > > > > As is fixes.2020.11.02a. > > > > > > > | git bisect good 1be6ab91e2db157faedb7f16ab0636a80745a073 > > > > | # good: [65e9eb1ccfe56b41a0d8bfec651ea014968413cb] rcu: Prevent RCU_LOCKDEP_WARN() from swallowing the condition > > > > > > And lockdep.2020.11.02a. > > > > > > > | git bisect good 65e9eb1ccfe56b41a0d8bfec651ea014968413cb > > > > | # good: [c386e29d43728778ddd642fa73cc582bee684171] docs/rcu: Update the call_rcu() API > > > > > > And doc.2020.11.06a. > > > > > > > | git bisect good c386e29d43728778ddd642fa73cc582bee684171 > > > > | # good: [27c0f1448389baf7f309b69e62d4b531c9395e88] rcutorture: Make grace-period kthread report match RCU flavor being tested > > > > > > And the first three commits of tasks.2020.11.06a. > > > > > > > | git bisect good 27c0f1448389baf7f309b69e62d4b531c9395e88 > > > > | # good: [3fcd6a230fa7d03bffcb831a81b40435c146c12b] x86/cpu: Avoid cpuinfo-induced IPIing of idle CPUs > > > > > > And cpuinfo.2020.11.06a. > > > > > > > | git bisect good 3fcd6a230fa7d03bffcb831a81b40435c146c12b > > > > | # good: [75dc2da5ecd65bdcbfc4d59b9d9b7342c61fe374] rcu-tasks: Make the units of ->init_fract be jiffies > > > > > > And the remaining commit of tasks.2020.11.06a. > > > > > > > | git bisect good 75dc2da5ecd65bdcbfc4d59b9d9b7342c61fe374 > > > > | # first bad commit: [765b512bb3d639bfad7dd43c288ee085236c7267] Merge branches 'cpuinfo.2020.11.06a', 'doc.2020.11.06a', 'fixes.2020.11.02a', 'lockdep.2020.11.02a', 'tasks.2020.11.06a' and 'torture.2020.11.06a' into HEAD > > > > > > > > This doesn't look very satisfying, given it's the merge commit. :-/ > > > > > > So each individual branch is just fine, but the merge of them is not. Fun. > > > > > > These have been passing quite a bit of rcutorture over here, including > > > preemptible kernels running !SMP, but admittedly on x86 rather than ARMv8. > > > > Note that this is ARMv8 on QEMU on an x86 host i.e. emulated. And it's > > really slow as a result. Together with a bunch of debug tools including > > lockdep. > > Then I don't envy you the bisection process! ;-) > > > > One approach would be to binary-search the combinations of merges. > > > Except that there are six of them, so there are 64 combinations, of > > > which you have tested only 8 thus far (none, one each, and all). > > > > > > But are you sure that the bisection points labeled "good" really are good? > > > For example, what is the distribution of first failure times in the > > > points labeled "bad" vs. the runtime used to make a "good" determination? > > > Alternatively, just try a longer run on each of the commits feeding into > > > the merge point. > > > > Yeah, I'm having doubts, and this might be even more non-deterministic > > that I thought and some 'good' could maybe be 'bad' if I had re-run > > them? I don't know. One thing I can try is to make sure I run it more > > than once, but I'm definitely not doing that manually, so let me try and > > script something so I don't have to hand-hold the bisection overnight. > > :-) > > I know that feeling. A similar experience motivated me to upgrade my > tooling, with more upgrades in the queue. [.....] > > > > | [ 841.143527] arch_local_irq_restore+0x4/0x8 > > > > > > So we are just now restoring interrupts, hence our getting the > > > interrupt at this point.. > > > > > > > | [ 841.147612] trace_preempt_on+0xf4/0x190 > > > > > > From within the trace code, which is apparently recording the fact > > > that preemption is being enabled. > > > > > > > | [ 841.151656] preempt_schedule_common+0x12c/0x1b0 > > > > | [ 841.155869] preempt_schedule.part.88+0x20/0x28 > > > > | [ 841.160036] preempt_schedule+0x20/0x28 > > > > > > I was not aware that releasing a raw spinlock could result in a direct > > > call to preempt_schedule(). > > > > > > > | [ 841.164051] _raw_spin_unlock_irq+0x80/0x90 > > > > | [ 841.168139] rcu_gp_kthread+0xe5c/0x19a8 > > > > > > So the RCU grace-period kthread has spent many seconds attempting to > > > release a lock? Am I reading this correctly? Mark Rutland, am I missing > > > something here? > > And yes, this is the RCU grace-period kthread releasing a lock. > > I have no idea why that would take so long. It is acting like a > self-deadlock or similar hang, except that in that case, lockdep should > have complained before the RCU CPU stall warning rather than after. > > The only thing I can suggest is sprinkling lockdep_assert_irqs_disabled() > calls hither and yon. All of the code that lockdep is complaining about > runs in the context of the scheduling-clock interrupt, so interrupts > had jolly well be disabled! ;-) > > Rerunning some of the allegedly good bisects might be more productive. Oof, so I reran bisection, and this time confirming 3x each good run. This is what I get: | git bisect start | # bad: [c07b306d7fa5680777e2132662d2e6c19fb53579] kfence: Avoid stalling work queue task without allocations | git bisect bad c07b306d7fa5680777e2132662d2e6c19fb53579 | # good: [3cea11cd5e3b00d91caf0b4730194039b45c5891] Linux 5.10-rc2 | git bisect good 27598e7e73260ed0b2917eb02d4a515ebb578313 | # good: [3e5acbea719e66ef3be64fe74c99cc905ca697dc] Merge remote-tracking branch 'wireless-drivers-next/master' into master | git bisect good 3e5acbea719e66ef3be64fe74c99cc905ca697dc | # good: [491a5a9a2fea28353d99621b8abb83b6928b4e36] Merge remote-tracking branch 'sound-asoc/for-next' into master | git bisect good 491a5a9a2fea28353d99621b8abb83b6928b4e36 | # bad: [502f8643d6e21c7e370a0b75131130cc51609055] Merge remote-tracking branch 'phy-next/next' into master | git bisect bad 502f8643d6e21c7e370a0b75131130cc51609055 | # good: [6693cb1fa5ea7b91ec00f9404776a095713face5] Merge remote-tracking branch 'tip/auto-latest' into master | git bisect good 6693cb1fa5ea7b91ec00f9404776a095713face5 | # good: [b790e3afead9357195b6d1e1b6cd9b3521503ad2] Merge branch 'tglx-pc.2020.10.30a' into HEAD | git bisect good b790e3afead9357195b6d1e1b6cd9b3521503ad2 | # bad: [7bd5bb161657717d576798f62b0e8d5b44653139] Merge remote-tracking branch 'drivers-x86/for-next' into master | git bisect bad 7bd5bb161657717d576798f62b0e8d5b44653139 | # bad: [e71eb4c4d42bcf36a3a7ede30fd320d47b3c8cb8] Merge remote-tracking branch 'xen-tip/linux-next' into master | git bisect bad e71eb4c4d42bcf36a3a7ede30fd320d47b3c8cb8 | # bad: [c0a41bf9dbc751692c8cb1a44bfd48e70e8bef7f] docs: Remove redundant "``" from Requirements.rst | git bisect bad c0a41bf9dbc751692c8cb1a44bfd48e70e8bef7f | # bad: [c293fb8f7de6c2fce11cb01a0218d668df326bcd] torture: Make --kcsan specify lockdep | git bisect bad c293fb8f7de6c2fce11cb01a0218d668df326bcd | # good: [5068ab7dcb6a526a401054ebe0d416f979efb3e1] rcutorture: Add testing for RCU's global memory ordering | git bisect good 5068ab7dcb6a526a401054ebe0d416f979efb3e1 | # good: [bea68a13bbbdc575a2c868dabd7b454c2eddc618] rcu/segcblist: Add additional comments to explain smp_mb() | git bisect good bea68a13bbbdc575a2c868dabd7b454c2eddc618 | # first bad commit: [c293fb8f7de6c2fce11cb01a0218d668df326bcd] torture: Make --kcsan specify lockdep Which clearly is ridiculous! So my guess is this probably had existed before, but something in -next is making it more visible. Short of giving up, I can try your suggestion of sprinkling lockdep_assert_irqs_disabled() everywhere, or if you have a patch to apply that would give some other debug output you wanted I can run that too. Thanks, -- Marco