From nobody Sun Feb 8 16:05:59 2026 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 DD1D2EB64DC for ; Mon, 17 Jul 2023 12:58:28 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231285AbjGQM61 (ORCPT ); Mon, 17 Jul 2023 08:58:27 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38796 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229972AbjGQM6J (ORCPT ); Mon, 17 Jul 2023 08:58:09 -0400 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 258E7170C; Mon, 17 Jul 2023 05:57:43 -0700 (PDT) Date: Mon, 17 Jul 2023 12:56:16 -0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1689598577; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=zlOkQCFk3GFnRbPmQXKHbRTdEl3oGUWoIOQ8kMbDV9I=; b=QcutTLYx3wmQOeYFDjLlFyjsINXg/Jxhca1Hrz9u/WAol1fdADWM4dmnRq40f+tnVesYts VWeUj+Us7M5cnIRG2LDrpZU3ZpzoJ4Hv78NE1w7UChz/dYLPkMuOFVBksUtxRYaEGlB0bE fEi3IkASmaS3shCHBTtd8xdEXWZKoSiqV3jk68youiL5gVe463i2d0dXfyTO08/4zM9+ri Kc0tFq1ZNoPY82njIdHWH3S4/vfkDgDrwaXE0/+5pNzcddlddqYDXTHIM0v8itzCQGtnCZ vnUOqBb590cO7NV9VrN3vdRyuhcQ/+glWSDYhx20hVJbBGX62+wLZAlTDgHegQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1689598577; h=from:from:sender:sender:reply-to:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=zlOkQCFk3GFnRbPmQXKHbRTdEl3oGUWoIOQ8kMbDV9I=; b=iS214HZ4+SeriTkWLWbI3D8WWXr2CNs3X5mTcVT24B7OVGtDor5LiUfayMSHC4uzXLWEUO IgqRtg1gJy/3hqBg== From: "tip-bot2 for Wander Lairson Costa" Sender: tip-bot2@linutronix.de Reply-to: linux-kernel@vger.kernel.org To: linux-tip-commits@vger.kernel.org Subject: [tip: sched/core] kernel/fork: beware of __put_task_struct() calling context Cc: Hu Chunyu , Oleg Nesterov , Valentin Schneider , Peter Zijlstra , Wander Lairson Costa , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20230614122323.37957-2-wander@redhat.com> References: <20230614122323.37957-2-wander@redhat.com> MIME-Version: 1.0 Message-ID: <168959857646.28540.11268009313059773705.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The following commit has been merged into the sched/core branch of tip: Commit-ID: d243b34459cea30cfe5f3a9b2feb44e7daff9938 Gitweb: https://git.kernel.org/tip/d243b34459cea30cfe5f3a9b2feb44e7d= aff9938 Author: Wander Lairson Costa AuthorDate: Wed, 14 Jun 2023 09:23:21 -03:00 Committer: Peter Zijlstra CommitterDate: Thu, 13 Jul 2023 15:21:48 +02:00 kernel/fork: beware of __put_task_struct() calling context 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 mark_lock+0x1e7/0x400 mark_usage+0x11d/0x140 __lock_acquire+0x30d/0x930 lock_acquire.part.0+0x9c/0x210 rt_spin_lock+0x27/0xe0 refill_obj_stock+0x3d/0x3a0 kmem_cache_free+0x357/0x560 inactive_task_timer+0x1ad/0x340 __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+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. The issue is reproducible with stress-ng: while true; do stress-ng --sched deadline --sched-period 1000000000 \ --sched-runtime 800000000 --sched-deadline \ 1000000000 --mmapfork 23 -t 20 done Reported-by: Hu Chunyu Suggested-by: Oleg Nesterov Suggested-by: Valentin Schneider Suggested-by: Peter Zijlstra Signed-off-by: Wander Lairson Costa Signed-off-by: Peter Zijlstra (Intel) Link: https://lore.kernel.org/r/20230614122323.37957-2-wander@redhat.com --- include/linux/sched/task.h | 28 +++++++++++++++++++++++++++- kernel/fork.c | 8 ++++++++ 2 files changed, 35 insertions(+), 1 deletion(-) diff --git a/include/linux/sched/task.h b/include/linux/sched/task.h index dd35ce2..6b687c1 100644 --- a/include/linux/sched/task.h +++ b/include/linux/sched/task.h @@ -118,10 +118,36 @@ static inline struct task_struct *get_task_struct(str= uct task_struct *t) } =20 extern void __put_task_struct(struct task_struct *t); +extern void __put_task_struct_rcu_cb(struct rcu_head *rhp); =20 static inline void put_task_struct(struct task_struct *t) { - if (refcount_dec_and_test(&t->usage)) + if (!refcount_dec_and_test(&t->usage)) + return; + + /* + * 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 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(). + */ + if (IS_ENABLED(CONFIG_PREEMPT_RT) && !preemptible()) + call_rcu(&t->rcu, __put_task_struct_rcu_cb); + else __put_task_struct(t); } =20 diff --git a/kernel/fork.c b/kernel/fork.c index d2e12b6..f811497 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -985,6 +985,14 @@ void __put_task_struct(struct task_struct *tsk) } EXPORT_SYMBOL_GPL(__put_task_struct); =20 +void __put_task_struct_rcu_cb(struct rcu_head *rhp) +{ + struct task_struct *task =3D container_of(rhp, struct task_struct, rcu); + + __put_task_struct(task); +} +EXPORT_SYMBOL_GPL(__put_task_struct_rcu_cb); + void __init __weak arch_task_cache_init(void) { } =20 /*