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[2620:137:e000::1:20]) by mx.google.com with ESMTP id x22-20020a17090a8a9600b002478a461fe6si16697583pjn.54.2023.04.26.10.50.41; Wed, 26 Apr 2023 10:50:56 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b=SlqezUK5; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239080AbjDZRpd (ORCPT + 99 others); Wed, 26 Apr 2023 13:45:33 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34602 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239049AbjDZRpb (ORCPT ); Wed, 26 Apr 2023 13:45:31 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C601635A5 for ; Wed, 26 Apr 2023 10:44:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1682531082; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=PFOLtpyLHj3LQRxvCiN2SdOhFROyPdkOD9iReg1b+zE=; b=SlqezUK5daOJ9cslzsv8AQ0SNutholTpLcPT7fVwDial9YMAwN4PUcFYMZHSskvvF80o55 4mu5G4FJ/i7yqbWiQugxiobJ9kz8ehjWxFkZXx4k6iK9Xg5YxSzx5jFsnIkvdU+6WfYxBJ 283YaZjQ/XhPXkTfyYQgaIr7eCb1UPI= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-345-uMUD12DJNoaicn7Sa1VlPg-1; Wed, 26 Apr 2023 13:44:37 -0400 X-MC-Unique: uMUD12DJNoaicn7Sa1VlPg-1 Received: from smtp.corp.redhat.com (int-mx09.intmail.prod.int.rdu2.redhat.com [10.11.54.9]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id F2A75101A550; Wed, 26 Apr 2023 17:44:35 +0000 (UTC) Received: from [10.22.18.92] (unknown [10.22.18.92]) by smtp.corp.redhat.com (Postfix) with ESMTP id 12DA0492C13; Wed, 26 Apr 2023 17:44:34 +0000 (UTC) Message-ID: <1ec831dd-1070-d1f0-1502-5b8e493caab0@redhat.com> Date: Wed, 26 Apr 2023 13:44:33 -0400 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.7.1 Subject: Re: [PATCH v7 0/3] Introduce put_task_struct_atomic_sleep() Content-Language: en-US To: Wander Lairson Costa , Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Ian Rogers , Adrian Hunter , Will Deacon , Boqun Feng , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Valentin Schneider , "Eric W. Biederman" , Huacai Chen , Geert Uytterhoeven , Oleg Nesterov , Kefeng Wang , Andrew Morton , "Liam R. Howlett" , Christian Brauner , Kees Cook , Andrei Vagin , Shakeel Butt , open list , "open list:PERFORMANCE EVENTS SUBSYSTEM" References: <20230425114307.36889-1-wander@redhat.com> From: Waiman Long In-Reply-To: <20230425114307.36889-1-wander@redhat.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 X-Spam-Status: No, score=-3.7 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,NICE_REPLY_A, RCVD_IN_DNSWL_NONE,RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE, T_SCC_BODY_TEXT_LINE autolearn=unavailable autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 4/25/23 07:43, Wander Lairson Costa wrote: > The put_task_struct() function reduces a usage counter and invokes > __put_task_struct() when the counter reaches zero. > > In the case of __put_task_struct(), it indirectly acquires a spinlock, > which operates as a sleeping lock under the PREEMPT_RT configuration. > As a result, invoking put_task_struct() within an atomic context is > not feasible for real-time (RT) kernels. > > One practical example is a splat inside inactive_task_timer(), which is > called in a interrupt context: > > CPU: 1 PID: 2848 Comm: life Kdump: loaded Tainted: G W --------- > Hardware name: HP ProLiant DL388p Gen8, BIOS P70 07/15/2012 > Call Trace: > dump_stack_lvl+0x57/0x7d > mark_lock_irq.cold+0x33/0xba > ? stack_trace_save+0x4b/0x70 > ? save_trace+0x55/0x150 > mark_lock+0x1e7/0x400 > mark_usage+0x11d/0x140 > __lock_acquire+0x30d/0x930 > lock_acquire.part.0+0x9c/0x210 > ? refill_obj_stock+0x3d/0x3a0 > ? rcu_read_lock_sched_held+0x3f/0x70 > ? trace_lock_acquire+0x38/0x140 > ? lock_acquire+0x30/0x80 > ? refill_obj_stock+0x3d/0x3a0 > rt_spin_lock+0x27/0xe0 > ? refill_obj_stock+0x3d/0x3a0 > refill_obj_stock+0x3d/0x3a0 > ? inactive_task_timer+0x1ad/0x340 > kmem_cache_free+0x357/0x560 > inactive_task_timer+0x1ad/0x340 > ? switched_from_dl+0x2d0/0x2d0 > __run_hrtimer+0x8a/0x1a0 > __hrtimer_run_queues+0x91/0x130 > hrtimer_interrupt+0x10f/0x220 > __sysvec_apic_timer_interrupt+0x7b/0xd0 > sysvec_apic_timer_interrupt+0x4f/0xd0 > ? asm_sysvec_apic_timer_interrupt+0xa/0x20 > asm_sysvec_apic_timer_interrupt+0x12/0x20 > RIP: 0033:0x7fff196bf6f5 > > To address this issue, this patch series introduces a new function > called put_task_struct_atomic_safe(). When compiled with the > PREEMPT_RT configuration, this function defers the call to > __put_task_struct() to a process context. > > Additionally, the patch series rectifies known problematic call sites > to ensure smooth functioning. > > Changelog > ========= > > v1: > * Initial implementation fixing the splat. > > v2: > * Isolate the logic in its own function. > * Fix two more cases caught in review. > > v3: > * Change __put_task_struct() to handle the issue internally. > > v4: > * Explain why call_rcu() is safe to call from interrupt context. > > v5: > * Explain why __put_task_struct() doesn't conflict with > put_task_sruct_rcu_user. > > v6: > * As per Sebastian's review, revert back the implementation of v2 > with a distinct function. > * Add a check in put_task_struct() to warning when called from a > non-sleepable context. > * Address more call sites. > > v7: > * Fix typos. > * Add an explanation why the new function doesn't conflict with > delayed_free_task(). > > Wander Lairson Costa (3): > sched/core: warn on call put_task_struct in invalid context > sched/task: Add the put_task_struct_atomic_safe() function > treewide: replace put_task_struct() with the atomic safe version > > include/linux/sched/task.h | 49 ++++++++++++++++++++++++++++++++++++++ > kernel/events/core.c | 6 ++--- > kernel/fork.c | 8 +++++++ > kernel/locking/rtmutex.c | 10 ++++---- > kernel/sched/core.c | 6 ++--- > kernel/sched/deadline.c | 16 ++++++------- > kernel/sched/rt.c | 4 ++-- > 7 files changed, 78 insertions(+), 21 deletions(-) This patch series looks good to me. Acked-by: Waiman Long I notice that __put_task_struct() invokes quite a bit of cleanup works from different subsystems. So it may burn quite a bit of cpu cycles to complete. This may not be something we want in an atomic context, maybe we should call call_rcu() irrespective of the PREEMPT_RT setting. Anyway, this can be a follow-up patch if we want to do that. Cheers, Longman