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[2620:137:e000::1:20]) by mx.google.com with ESMTP id sc24-20020a1709078a1800b007c079eed73csi32786670ejc.416.2023.01.04.10.31.17; Wed, 04 Jan 2023 10:31:42 -0800 (PST) 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=Av1hYKM9; 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 S235259AbjADSSB (ORCPT + 99 others); Wed, 4 Jan 2023 13:18:01 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35570 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230341AbjADSR6 (ORCPT ); Wed, 4 Jan 2023 13:17:58 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6883F186F4 for ; Wed, 4 Jan 2023 10:17:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1672856232; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=7eWASEchnGHOlz8RYd1duNxZ3+6gs7X9NPG+qDh7uMQ=; b=Av1hYKM9okQAP7+tjbkT6YZsEAH92r5RXdZJpLAZxTMRGTLDzlnEcfEB7QDZo/NSLnYPnS 86YTw9ikp/vZvcjWbKZDTUehD9kyinB170ZUHZbvbiR52n++M0R55p3GFw1zRJ3t2I6duT 5b0v0UDG+mv/antfAckBwetL+xWAQ40= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-650-qN5_tDt-P7Gyp0csf8iaxg-1; Wed, 04 Jan 2023 13:17:08 -0500 X-MC-Unique: qN5_tDt-P7Gyp0csf8iaxg-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 0AB91299E752; Wed, 4 Jan 2023 18:17:08 +0000 (UTC) Received: from fedora.redhat.com (unknown [10.22.32.228]) by smtp.corp.redhat.com (Postfix) with ESMTP id 66B59492B06; Wed, 4 Jan 2023 18:17:04 +0000 (UTC) From: Wander Lairson Costa To: Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Valentin Schneider , linux-kernel@vger.kernel.org (open list:SCHEDULER) Cc: Wander Lairson Costa , Paul McKenney , Thomas Gleixner Subject: [PATCH] sched/deadline: fix inactive_task_timer splat with CONFIG_PREEMPT_RT Date: Wed, 4 Jan 2023 15:17:01 -0300 Message-Id: <20230104181701.43224-1-wander@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.9 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE autolearn=ham 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 X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1754117808647431678?= X-GMAIL-MSGID: =?utf-8?q?1754117808647431678?= inactive_task_timer() executes in interrupt (atomic) context. It calls put_task_struct(), which indirectly acquires sleeping locks under PREEMPT_RT. Below is an example of a splat that happened in a test environment: 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 Instead of calling put_task_struct() directly, we defer it using call_rcu(). A more natural approach would use a workqueue, but since in PREEMPT_RT, we can't allocate dynamic memory from atomic context, the code would become more complex because we would need to put the work_struct instance in the task_struct and initialize it when we allocate a new task_struct. Signed-off-by: Wander Lairson Costa Cc: Paul McKenney Cc: Thomas Gleixner Reviewed-by: Valentin Schneider --- kernel/sched/build_policy.c | 1 + kernel/sched/deadline.c | 24 +++++++++++++++++++++++- 2 files changed, 24 insertions(+), 1 deletion(-) diff --git a/kernel/sched/build_policy.c b/kernel/sched/build_policy.c index d9dc9ab3773f..f159304ee792 100644 --- a/kernel/sched/build_policy.c +++ b/kernel/sched/build_policy.c @@ -28,6 +28,7 @@ #include #include #include +#include #include diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c index 9ae8f41e3372..ab9301d4cc24 100644 --- a/kernel/sched/deadline.c +++ b/kernel/sched/deadline.c @@ -1405,6 +1405,13 @@ static void update_curr_dl(struct rq *rq) } } +static void delayed_put_task_struct(struct rcu_head *rhp) +{ + struct task_struct *task = container_of(rhp, struct task_struct, rcu); + + __put_task_struct(task); +} + static enum hrtimer_restart inactive_task_timer(struct hrtimer *timer) { struct sched_dl_entity *dl_se = container_of(timer, @@ -1442,7 +1449,22 @@ static enum hrtimer_restart inactive_task_timer(struct hrtimer *timer) dl_se->dl_non_contending = 0; unlock: task_rq_unlock(rq, p, &rf); - put_task_struct(p); + + if (IS_ENABLED(CONFIG_PREEMPT_RT)) { + /* + * Decrement the refcount explicitly to avoid unnecessarily + * calling call_rcu. + */ + if (refcount_dec_and_test(&p->usage)) + /* + * under PREEMPT_RT, we can't call put_task_struct + * in atomic context because it will indirectly + * acquire sleeping locks. + */ + call_rcu(&p->rcu, delayed_put_task_struct); + } else { + put_task_struct(p); + } return HRTIMER_NORESTART; }