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 42901C77B6E for ; Fri, 14 Apr 2023 12:57:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229689AbjDNM5A (ORCPT ); Fri, 14 Apr 2023 08:57:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40188 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229907AbjDNM46 (ORCPT ); Fri, 14 Apr 2023 08:56:58 -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 8B089A276 for ; Fri, 14 Apr 2023 05:56:15 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1681476974; 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=vWFEUBEXcCftzEc0hD+kF0Un2IVbNKstSMRg6ONrT+s=; b=Bu1QQ1gzXI5UIYpSfxRKfb1qZ767MXaaDbkeC5kMak8l4aN4Sm6r0LM2WMc0zUTIrzg93L X1hqim0RAKVoJWmLxOo9X/xeOEkrP0HpXFQvOo8Ez5CBZTLO8JLDbtRx2Ztrhfy5YdMFXE um2Ll2iGPv2CDL/hYmrgQSCdqRsjIaU= 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-265-7T0V0wkQOSK6KOzPfQ9_AQ-1; Fri, 14 Apr 2023 08:56:07 -0400 X-MC-Unique: 7T0V0wkQOSK6KOzPfQ9_AQ-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 3B6FA185A790; Fri, 14 Apr 2023 12:56:06 +0000 (UTC) Received: from fedora.redhat.com (unknown [10.22.9.8]) by smtp.corp.redhat.com (Postfix) with ESMTP id 28918406AA66; Fri, 14 Apr 2023 12:55:59 +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 , Michael Ellerman , Andrew Morton , Oleg Nesterov , Kefeng Wang , "Liam R. Howlett" , Kees Cook , 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 v6 2/3] sched/task: Add the put_task_struct_atomic_safe() function Date: Fri, 14 Apr 2023 09:55:28 -0300 Message-Id: <20230414125532.14958-3-wander@redhat.com> In-Reply-To: <20230414125532.14958-1-wander@redhat.com> References: <20230414125532.14958-1-wander@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.1 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 Cc: Paul McKenney Cc: Thomas Gleixner --- include/linux/sched/task.h | 31 +++++++++++++++++++++++++++++++ kernel/fork.c | 8 ++++++++ 2 files changed, 39 insertions(+) diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h index b597b97b1f8f..5c13b83d7008 100644 --- a/include/linux/sched/task.h +++ b/include/linux/sched/task.h @@ -141,6 +141,37 @@ 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_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(&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 0c92f224c68c..9884794fe4b8 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) { } /* -- 2.39.2