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=-7.1 required=3.0 tests=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 E2C07C433E1 for ; Tue, 23 Jun 2020 19:34:35 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BE7BE2098B for ; Tue, 23 Jun 2020 19:34:35 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=joelfernandes.org header.i=@joelfernandes.org header.b="tUR9PvFC" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387453AbgFWTee (ORCPT ); Tue, 23 Jun 2020 15:34:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45192 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1733270AbgFWTed (ORCPT ); Tue, 23 Jun 2020 15:34:33 -0400 Received: from mail-qt1-x841.google.com (mail-qt1-x841.google.com [IPv6:2607:f8b0:4864:20::841]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 90F65C061755 for ; Tue, 23 Jun 2020 12:34:33 -0700 (PDT) Received: by mail-qt1-x841.google.com with SMTP id g13so5966543qtv.8 for ; Tue, 23 Jun 2020 12:34:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=joelfernandes.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=1KH0rH4AzuBPYQeNW5blpz22/GCRUG77096zZyppVno=; b=tUR9PvFC3GgnpjVtmtnBBlPb+Ew1cd1NhAJa3TjHqvezwd9XwE4uo2OQ7hQISqZF0Y VxPD1iR1R6wecw9ysY6xSnD2CsciZsNd/4xhVH0YuKzKkU7hg9xwNNBJ83Adnz2YpmyP urm15SXUQpcsMuSrFBW7iZAunMQWLUzPHcPmY= 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; bh=1KH0rH4AzuBPYQeNW5blpz22/GCRUG77096zZyppVno=; b=LnaNw9ftINt7u5axxtTmmu3/dftRiQPNrbLlCFbtD3Euf/PpYTa3luZ3gK/a1RVCaG HCdw+7cDM3mhJA31fga8uFZQtM1kWO5AIxdfvZm3m0RF0bO0LBdD5zsdmNyUsL7WksWv W8CoSgPSmgAHRGU+0YDLZNyzgxomBthbhBX4RtQWOiCsED8gb5KoRtYVYNDvGa4QqlTD C71hlYd/sOf/emAE90NTF+PCU9b3vZ5w9+/DZncWQ6q24JIV7U9zhQkOfY/xUcen6OJY OwOeilWcYh02kK9jUQNTXIbb4g/6EMoRv7QnfjWT1AH79Q8jTKPKFioOUBlqyjXOMc8l P8Kg== X-Gm-Message-State: AOAM532CEYSBD3/jRI6UIqE1bd3X6zw+bMQfQbYdcpevSFdlvzVCZ92k azCdZsXZ/+ZkvQgxy5rO7XKR/A== X-Google-Smtp-Source: ABdhPJyODTmkyFeqdCWZE2FRa+eXXwdEG2dXmWJq2l+EEmDpeSfVft+TA5lSLgNAhYOl9TJtOShCIA== X-Received: by 2002:ac8:4507:: with SMTP id q7mr21352369qtn.142.1592940872546; Tue, 23 Jun 2020 12:34:32 -0700 (PDT) Received: from localhost ([2620:15c:6:12:9c46:e0da:efbf:69cc]) by smtp.gmail.com with ESMTPSA id v69sm1375392qkb.96.2020.06.23.12.34.31 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 23 Jun 2020 12:34:31 -0700 (PDT) Date: Tue, 23 Jun 2020 15:34:31 -0400 From: Joel Fernandes To: paulmck@kernel.org Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, linux-mm@kvack.org Subject: Re: [PATCH tip/core/rcu 02/26] mm/mmap.c: Add cond_resched() for exit_mmap() CPU stalls Message-ID: <20200623193431.GA68372@google.com> References: <20200623002128.GA25456@paulmck-ThinkPad-P72> <20200623002147.25750-2-paulmck@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200623002147.25750-2-paulmck@kernel.org> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 22, 2020 at 05:21:23PM -0700, paulmck@kernel.org wrote: > From: "Paul E. McKenney" > > A large process running on a heavily loaded system can encounter the > following RCU CPU stall warning: > > rcu: INFO: rcu_sched self-detected stall on CPU > rcu: \x093-....: (20998 ticks this GP) idle=4ea/1/0x4000000000000002 softirq=556558/556558 fqs=5190 > \x09(t=21013 jiffies g=1005461 q=132576) > NMI backtrace for cpu 3 > CPU: 3 PID: 501900 Comm: aio-free-ring-w Kdump: loaded Not tainted 5.2.9-108_fbk12_rc3_3858_gb83b75af7909 #1 > Hardware name: Wiwynn HoneyBadger/PantherPlus, BIOS HBM6.71 02/03/2016 > Call Trace: > > dump_stack+0x46/0x60 > nmi_cpu_backtrace.cold.3+0x13/0x50 > ? lapic_can_unplug_cpu.cold.27+0x34/0x34 > nmi_trigger_cpumask_backtrace+0xba/0xca > rcu_dump_cpu_stacks+0x99/0xc7 > rcu_sched_clock_irq.cold.87+0x1aa/0x397 > ? tick_sched_do_timer+0x60/0x60 > update_process_times+0x28/0x60 > tick_sched_timer+0x37/0x70 > __hrtimer_run_queues+0xfe/0x270 > hrtimer_interrupt+0xf4/0x210 > smp_apic_timer_interrupt+0x5e/0x120 > apic_timer_interrupt+0xf/0x20 > > RIP: 0010:kmem_cache_free+0x223/0x300 > Code: 88 00 00 00 0f 85 ca 00 00 00 41 8b 55 18 31 f6 f7 da 41 f6 45 0a 02 40 0f 94 c6 83 c6 05 9c 41 5e fa e8 a0 a7 01 00 41 56 9d <49> 8b 47 08 a8 03 0f 85 87 00 00 00 65 48 ff 08 e9 3d fe ff ff 65 > RSP: 0018:ffffc9000e8e3da8 EFLAGS: 00000206 ORIG_RAX: ffffffffffffff13 > RAX: 0000000000020000 RBX: ffff88861b9de960 RCX: 0000000000000030 > RDX: fffffffffffe41e8 RSI: 000060777fe3a100 RDI: 000000000001be18 > RBP: ffffea00186e7780 R08: ffffffffffffffff R09: ffffffffffffffff > R10: ffff88861b9dea28 R11: ffff88887ffde000 R12: ffffffff81230a1f > R13: ffff888854684dc0 R14: 0000000000000206 R15: ffff8888547dbc00 > ? remove_vma+0x4f/0x60 > remove_vma+0x4f/0x60 > exit_mmap+0xd6/0x160 > mmput+0x4a/0x110 > do_exit+0x278/0xae0 > ? syscall_trace_enter+0x1d3/0x2b0 > ? handle_mm_fault+0xaa/0x1c0 > do_group_exit+0x3a/0xa0 > __x64_sys_exit_group+0x14/0x20 > do_syscall_64+0x42/0x100 > entry_SYSCALL_64_after_hwframe+0x44/0xa9 > > And on a PREEMPT=n kernel, the "while (vma)" loop in exit_mmap() can run > for a very long time given a large process. This commit therefore adds > a cond_resched() to this loop, providing RCU any needed quiescent states. > > Cc: Andrew Morton > Cc: > Signed-off-by: Paul E. McKenney > --- > mm/mmap.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/mmap.c b/mm/mmap.c > index 59a4682..972f839 100644 > --- a/mm/mmap.c > +++ b/mm/mmap.c > @@ -3159,6 +3159,7 @@ void exit_mmap(struct mm_struct *mm) > if (vma->vm_flags & VM_ACCOUNT) > nr_accounted += vma_pages(vma); > vma = remove_vma(vma); > + cond_resched(); Reviewed-by: Joel Fernandes (Google) Just for my understanding, cond_resched_tasks_rcu_qs() may not help here because preemption is not disabled right? Still I see no harm in using it here either as it may give a slight speed up for tasks-RCU. thanks, - Joel > } > vm_unacct_memory(nr_accounted); > } > -- > 2.9.5 >