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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id E00E2C77B61 for ; Tue, 25 Apr 2023 11:44:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233922AbjDYLop (ORCPT ); Tue, 25 Apr 2023 07:44:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:45214 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233774AbjDYLoo (ORCPT ); Tue, 25 Apr 2023 07:44:44 -0400 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 904DD49CB for ; Tue, 25 Apr 2023 04:43:59 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1682423038; 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: in-reply-to:in-reply-to:references:references; bh=U265zX8tq5WfRp+xioeBIGxCCS4jZo0GQceEaEesDaM=; b=fYvso+zoaFzP7chadqeNbAZLqjpwcjUMFi6PcdfB+wY9cUGbw2AW0KuqmuZ2IZb0NJDank tam91nOGRGj+fp8rqYVUqZ5HdDMZc/AWJ53BPDordEWmKKDMDMAlQ/qoeCrQAr95RmOCSH 5VSSUxwCo1RUTs8CBe5bHZGFnNdAhq4= 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-536-Wt_spITUMDODh06iTe24Og-1; Tue, 25 Apr 2023 07:43:54 -0400 X-MC-Unique: Wt_spITUMDODh06iTe24Og-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.rdu2.redhat.com [10.11.54.8]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 4A6DE3C11783; Tue, 25 Apr 2023 11:43:53 +0000 (UTC) Received: from fedora.redhat.com (unknown [10.22.32.181]) by smtp.corp.redhat.com (Postfix) with ESMTP id C629DC15BA0; Tue, 25 Apr 2023 11:43:45 +0000 (UTC) From: Wander Lairson Costa To: Peter Zijlstra , Ingo Molnar , Arnaldo Carvalho de Melo , Mark Rutland , Alexander Shishkin , Jiri Olsa , Namhyung Kim , Ian Rogers , Adrian Hunter , Will Deacon , Waiman Long , Boqun Feng , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Valentin Schneider , "Eric W. Biederman" , Wander Lairson Costa , Oleg Nesterov , Brian Cain , Kefeng Wang , Andrew Morton , "Liam R. Howlett" , Vlastimil Babka , Christian Brauner , Andrei Vagin , Shakeel Butt , linux-kernel@vger.kernel.org (open list), linux-perf-users@vger.kernel.org (open list:PERFORMANCE EVENTS SUBSYSTEM) Cc: Hu Chunyu , Paul McKenney , Thomas Gleixner Subject: [PATCH v7 2/3] sched/task: Add the put_task_struct_atomic_safe() function Date: Tue, 25 Apr 2023 08:43:02 -0300 Message-Id: <20230425114307.36889-3-wander@redhat.com> In-Reply-To: <20230425114307.36889-1-wander@redhat.com> References: <20230425114307.36889-1-wander@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.8 Precedence: bulk List-ID: X-Mailing-List: linux-perf-users@vger.kernel.org Due to the possibility of indirectly acquiring sleeping locks, it is unsafe to call put_task_struct() in atomic contexts when the kernel is compiled with PREEMPT_RT. To mitigate this issue, this commit introduces put_task_struct_atomic_safe(), which schedules __put_task_struct() through call_rcu() when PREEMPT_RT is enabled. While a workqueue would be a more natural approach, we cannot allocate dynamic memory from atomic context in PREEMPT_RT, making the code more complex. This implementation ensures safe execution in atomic contexts and avoids any potential issues that may arise from using the non-atomic version. Signed-off-by: Wander Lairson Costa Reported-by: Hu Chunyu Reviewed-by: Paul McKenney Cc: Thomas Gleixner --- include/linux/sched/task.h | 35 +++++++++++++++++++++++++++++++++++ kernel/fork.c | 8 ++++++++ 2 files changed, 43 insertions(+) diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h index b597b97b1f8f..cf774b83b2ec 100644 --- a/include/linux/sched/task.h +++ b/include/linux/sched/task.h @@ -141,6 +141,41 @@ static inline void put_task_struct_many(struct task_struct *t, int nr) void put_task_struct_rcu_user(struct task_struct *task); +extern void __delayed_put_task_struct(struct rcu_head *rhp); + +static inline void put_task_struct_atomic_safe(struct task_struct *task) +{ + if (IS_ENABLED(CONFIG_PREEMPT_RT)) { + /* + * Decrement the refcount explicitly to avoid unnecessarily + * calling call_rcu. + */ + if (refcount_dec_and_test(&task->usage)) + /* + * 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() + * to be called in process context. + * + * __put_task_struct() is 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. + * + * delayed_free_task() also uses ->rcu, but it is only called + * when it fails to fork a process. Therefore, there is no + * way it can conflict with put_task_struct(). + */ + call_rcu(&task->rcu, __delayed_put_task_struct); + } else { + put_task_struct(task); + } +} + /* Free all architecture-specific resources held by a thread. */ void release_thread(struct task_struct *dead_task); diff --git a/kernel/fork.c b/kernel/fork.c index ea332319dffe..7f016b691b1d 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -854,6 +854,14 @@ void __put_task_struct(struct task_struct *tsk) } EXPORT_SYMBOL_GPL(__put_task_struct); +void __delayed_put_task_struct(struct rcu_head *rhp) +{ + struct task_struct *task = container_of(rhp, struct task_struct, rcu); + + __put_task_struct(task); +} +EXPORT_SYMBOL_GPL(__delayed_put_task_struct); + void __init __weak arch_task_cache_init(void) { } /* -- 2.40.0