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=-9.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 249CFC388F7 for ; Tue, 10 Nov 2020 23:23:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CEBE2207BB for ; Tue, 10 Nov 2020 23:23:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=linaro.org header.i=@linaro.org header.b="uSONrwvL" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732119AbgKJXXg (ORCPT ); Tue, 10 Nov 2020 18:23:36 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59696 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726706AbgKJXXg (ORCPT ); Tue, 10 Nov 2020 18:23:36 -0500 Received: from mail-lf1-x143.google.com (mail-lf1-x143.google.com [IPv6:2a00:1450:4864:20::143]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E4D17C0613D1 for ; Tue, 10 Nov 2020 15:23:35 -0800 (PST) Received: by mail-lf1-x143.google.com with SMTP id w142so554885lff.8 for ; Tue, 10 Nov 2020 15:23:34 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=snmzgSJawG90tTENS8PRBQJwFI4U/+eiuWYIm1kFYpU=; b=uSONrwvLS562QD778AZnBzkL2b13eJTCpIkg8DZEkUeeam0tmYKKSBV/kx+uOLHdVf ZNnXB/UORVGeRUKcXKSZxusE4kthAsy5euuYRLWjoj6YJFAio7Yo7jI4DyUkdtlzFXpB 2B3bs5jUETOsb5quhJyXAI89PX+HdfqMtfHJxcJYsq++Xd0giVPV4gNfMSJi7AzFzGLW 8LcMaLXUnkhVOhjAMteowWEowIW7Za5GTFrVilW4l+Hs4/z22dy7TOBeRVIin+9KVhcm 2GTzcNXnwZba1hzZ9rvBz+De1lTWmjjWAX0flo1w1A8OAZDOKElAu0nuVU0AUhE9teHy bi6g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=snmzgSJawG90tTENS8PRBQJwFI4U/+eiuWYIm1kFYpU=; b=iB2lOsvTKf/juuYEXf2U9B5Bp74iDmLPOZ5nFeC+PAFOLu7vBvKEReBtluj91G5nB0 6MhS5KRIDapi971NXtEcacFE48WBARK1QvpAOChbSAguOtEO+NmNl2yABNp9jxsh8LUJ PeKMeIhtR857nMnYJo0CQuc6H6yX5NNFF2indrcVvWtvB3vVMbicMQySyi5jFR2MupFs TZ20uSyAOg9npK7Ie+H1JhpeVCc+HKI40KptyMgC6AAIg49u1YXHEpVY3F4kfTkhf1yx qHIVeoDPWrGuq9E+XxHHw7TEJ1jY+fTztnODf2yhIT2TA9j29r4/80kpgTkU0QpEXKLF LFZg== X-Gm-Message-State: AOAM530+zh9oV8WTcPfkJW2jB3B5vmg5w6J7zrJuH4/TfDK6mxvnh1R8 ixwAM3OzxLn17Mx7Ew7q8Cf91aQyUBZQi4VYbN4ypw== X-Google-Smtp-Source: ABdhPJyS2NN9tRpqxcU5Fpkjh4lEZ2YMoIh1E9ka9q+9o1Kwp0lXj/r2Bw0pDxM3hW0UCgzMs/mXFiJZPs+iIgibWVM= X-Received: by 2002:a19:40c7:: with SMTP id n190mr2214361lfa.185.1605050605523; Tue, 10 Nov 2020 15:23:25 -0800 (PST) MIME-Version: 1.0 References: <20201110135320.3309507-1-elver@google.com> In-Reply-To: <20201110135320.3309507-1-elver@google.com> From: Anders Roxell Date: Wed, 11 Nov 2020 00:23:14 +0100 Message-ID: Subject: Re: [PATCH] kfence: Avoid stalling work queue task without allocations To: Marco Elver Cc: Andrew Morton , Alexander Potapenko , Dmitry Vyukov , Jann Horn , Mark Rutland , Linux Kernel Mailing List , Linux-MM , kasan-dev Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 10 Nov 2020 at 14:53, Marco Elver wrote: > > To toggle the allocation gates, we set up a delayed work that calls > toggle_allocation_gate(). Here we use wait_event() to await an > allocation and subsequently disable the static branch again. However, if > the kernel has stopped doing allocations entirely, we'd wait > indefinitely, and stall the worker task. This may also result in the > appropriate warnings if CONFIG_DETECT_HUNG_TASK=y. > > Therefore, introduce a 1 second timeout and use wait_event_timeout(). If > the timeout is reached, the static branch is disabled and a new delayed > work is scheduled to try setting up an allocation at a later time. > > Note that, this scenario is very unlikely during normal workloads once > the kernel has booted and user space tasks are running. It can, however, > happen during early boot after KFENCE has been enabled, when e.g. > running tests that do not result in any allocations. > > Link: https://lkml.kernel.org/r/CADYN=9J0DQhizAGB0-jz4HOBBh+05kMBXb4c0cXMS7Qi5NAJiw@mail.gmail.com > Reported-by: Anders Roxell > Signed-off-by: Marco Elver > --- > mm/kfence/core.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/mm/kfence/core.c b/mm/kfence/core.c > index 9358f42a9a9e..933b197b8634 100644 > --- a/mm/kfence/core.c > +++ b/mm/kfence/core.c > @@ -592,7 +592,11 @@ static void toggle_allocation_gate(struct work_struct *work) > /* Enable static key, and await allocation to happen. */ > atomic_set(&allocation_gate, 0); > static_branch_enable(&kfence_allocation_key); > - wait_event(allocation_wait, atomic_read(&allocation_gate) != 0); > + /* > + * Await an allocation. Timeout after 1 second, in case the kernel stops > + * doing allocations, to avoid stalling this worker task for too long. > + */ > + wait_event_timeout(allocation_wait, atomic_read(&allocation_gate) != 0, HZ); > > /* Disable static key and reset timer. */ > static_branch_disable(&kfence_allocation_key); > -- > 2.29.2.222.g5d2a92d10f8-goog > I gave them a spin on next-20201105 [1] and on next-20201110 [2]. I eventually got to a prompt on next-20201105. However, I got to this kernel panic on the next-20201110: [...] [ 1514.089966][ T1] Testing event system initcall: OK [ 1514.806232][ T1] Running tests on all trace events: [ 1514.857835][ T1] Testing all events: [ 1525.503262][ C0] hrtimer: interrupt took 10902600 ns [ 1623.861452][ C0] BUG: workqueue lockup - pool cpus=0 node=0 flags=0x0 nice=0 stuck for 65s! [...] [ 7823.104349][ T28] Tainted: G W 5.10.0-rc3-next-20201110-00008-g8dc06700529d #3 [ 7833.206491][ T28] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 7840.750700][ T28] task:kworker/0:1 state:D stack:26640 pid: 1872 ppid: 2 flags:0x00000428 [ 7875.642531][ T28] Workqueue: events toggle_allocation_gate [ 7889.178334][ T28] Call trace: [ 7897.066649][ T28] __switch_to+0x1cc/0x1e0 [ 7905.326856][ T28] 0xffff00000f7077b0 [ 7928.354644][ T28] INFO: lockdep is turned off. [ 7934.022572][ T28] Kernel panic - not syncing: hung_task: blocked tasks [ 7934.032039][ T28] CPU: 0 PID: 28 Comm: khungtaskd Tainted: G W 5.10.0-rc3-next-20201110-00008-g8dc06700529d #3 [ 7934.045586][ T28] Hardware name: linux,dummy-virt (DT) [ 7934.053677][ T28] Call trace: [ 7934.060276][ T28] dump_backtrace+0x0/0x420 [ 7934.067635][ T28] show_stack+0x38/0xa0 [ 7934.091277][ T28] dump_stack+0x1d4/0x278 [ 7934.098878][ T28] panic+0x304/0x5d8 [ 7934.114923][ T28] check_hung_uninterruptible_tasks+0x5e4/0x640 [ 7934.123823][ T28] watchdog+0x138/0x160 [ 7934.131561][ T28] kthread+0x23c/0x260 [ 7934.138590][ T28] ret_from_fork+0x10/0x18 [ 7934.146631][ T28] Kernel Offset: disabled [ 7934.153749][ T28] CPU features: 0x0240002,20002004 [ 7934.161476][ T28] Memory Limit: none [ 7934.171272][ T28] ---[ end Kernel panic - not syncing: hung_task: blocked tasks ]--- Cheers, Anders [1] https://people.linaro.org/~anders.roxell/output-next-20201105-test.log [2] https://people.linaro.org/~anders.roxell/output-next-20201110-test.log