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[2620:137:e000::1:20]) by mx.google.com with ESMTP id u23-20020a170906109700b0087bda7465bcsi6889276eju.844.2023.02.10.08.19.58; Fri, 10 Feb 2023 08:20:21 -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="APA/rn0t"; 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 S232706AbjBJQOS (ORCPT + 99 others); Fri, 10 Feb 2023 11:14:18 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:35808 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232730AbjBJQOQ (ORCPT ); Fri, 10 Feb 2023 11:14:16 -0500 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 6E8F5305DD for ; Fri, 10 Feb 2023 08:13:34 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1676045613; 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=Pw9sqy2tAS5AGgdpXQ3blupZ5RHaig7ePYhZjFr/r3s=; b=APA/rn0tWeUDx+DbXpIpR24TWFfGBr6orO+m1wuEvcvcDn9U7HEGVKpwgdAW0LEYuoLPqD 1MMgSsPmzR5D/IDyhrOrsCNuP9nVc84UoZruwC9w30ij/d0rg6YkZPntZ0WVvtP/tEflIk eG4326wPywMj/5wbZ5LapfMCc8dbTBw= 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-623-hhcEo0GKO6m4ggIlWzVIPA-1; Fri, 10 Feb 2023 11:13:32 -0500 X-MC-Unique: hhcEo0GKO6m4ggIlWzVIPA-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 8EFB285A5B1; Fri, 10 Feb 2023 16:13:31 +0000 (UTC) Received: from fedora.redhat.com (unknown [10.22.18.44]) by smtp.corp.redhat.com (Postfix) with ESMTP id 15B3A492C3F; Fri, 10 Feb 2023 16:13:26 +0000 (UTC) From: Wander Lairson Costa To: Andrew Morton , Thomas Gleixner , "Eric W. Biederman" , Andy Lutomirski , Sebastian Andrzej Siewior , "Liam R. Howlett" , Peter Zijlstra , Fenghua Yu , Wander Lairson Costa , Andrei Vagin , linux-kernel@vger.kernel.org (open list) Cc: Hu Chunyu , Oleg Nesterov , Valentin Schneider , Paul McKenney Subject: [PATCH v5] kernel/fork: beware of __put_task_struct calling context Date: Fri, 10 Feb 2023 13:13:21 -0300 Message-Id: <20230210161323.37400-1-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?1757461632379908553?= X-GMAIL-MSGID: =?utf-8?q?1757461632379908553?= Under PREEMPT_RT, __put_task_struct() indirectly acquires sleeping locks. Therefore, it can't be called from an non-preemptible context. One practical example is 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 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. 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. Signed-off-by: Wander Lairson Costa Reported-by: Hu Chunyu Suggested-by: Oleg Nesterov Suggested-by: Valentin Schneider Cc: Paul McKenney --- kernel/fork.c | 33 ++++++++++++++++++++++++++++++++- 1 file changed, 32 insertions(+), 1 deletion(-) diff --git a/kernel/fork.c b/kernel/fork.c index 9f7fe3541897..9bf30c725ed8 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -840,7 +840,7 @@ static inline void put_signal_struct(struct signal_struct *sig) free_signal_struct(sig); } -void __put_task_struct(struct task_struct *tsk) +static void ___put_task_struct(struct task_struct *tsk) { WARN_ON(!tsk->exit_state); WARN_ON(refcount_read(&tsk->usage)); @@ -857,6 +857,37 @@ void __put_task_struct(struct task_struct *tsk) sched_core_free(tsk); free_task(tsk); } + +static void __put_task_struct_rcu(struct rcu_head *rhp) +{ + struct task_struct *task = container_of(rhp, struct task_struct, rcu); + + ___put_task_struct(task); +} + +void __put_task_struct(struct task_struct *tsk) +{ + if (IS_ENABLED(CONFIG_PREEMPT_RT) && (!preemptible() || !in_task())) + /* + * under PREEMPT_RT, we can't call put_task_struct + * in atomic context because it will indirectly + * acquire sleeping locks. + * + * call_rcu() will schedule delayed_put_task_struct_rcu() + * to be called in process context. + * + * __put_task_struct() is called called when + * refcount_dec_and_test(&t->usage) succeeds. + * + * This means that it can't "conflict" with + * put_task_struct_rcu_user() which abuses ->rcu the same + * way; rcu_users has a reference so task->usage can't be + * zero after rcu_users 1 -> 0 transition. + */ + call_rcu(&tsk->rcu, __put_task_struct_rcu); + else + ___put_task_struct(tsk); +} EXPORT_SYMBOL_GPL(__put_task_struct); void __init __weak arch_task_cache_init(void) { }