From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933049AbcFOVrm (ORCPT ); Wed, 15 Jun 2016 17:47:42 -0400 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:44603 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753664AbcFOVqU (ORCPT ); Wed, 15 Jun 2016 17:46:20 -0400 X-IBM-Helo: d03dlp03.boulder.ibm.com X-IBM-MailFrom: paulmck@linux.vnet.ibm.com X-IBM-RcptTo: linux-kernel@vger.kernel.org From: "Paul E. McKenney" To: linux-kernel@vger.kernel.org Cc: mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, dvhart@linux.intel.com, fweisbec@gmail.com, oleg@redhat.com, bobby.prani@gmail.com, "Paul E. McKenney" Subject: [PATCH tip/core/rcu 09/12] rcu: Make call_rcu_tasks() tolerate first call with irqs disabled Date: Wed, 15 Jun 2016 14:46:10 -0700 X-Mailer: git-send-email 2.5.2 In-Reply-To: <20160615214550.GA4931@linux.vnet.ibm.com> References: <20160615214550.GA4931@linux.vnet.ibm.com> X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16061521-0012-0000-0000-00000FF24B72 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16061521-0013-0000-0000-000042C72E17 Message-Id: <1466027173-5501-9-git-send-email-paulmck@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-06-15_13:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=3 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1604210000 definitions=main-1606150231 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Currently, if the very first call to call_rcu_tasks() has irqs disabled, it will create the rcu_tasks_kthread with irqs disabled, which will result in a splat in the memory allocator, which kthread_run() invokes with the expectation that irqs are enabled. This commit fixes this problem by deferring kthread creation if called with irqs disabled. The first call to call_rcu_tasks() that has irqs enabled will create the kthread. This bug was detected by rcutorture changes that were motivated by Iftekhar Ahmed's mutation-testing efforts. Signed-off-by: Paul E. McKenney --- include/linux/rcupdate.h | 1 + kernel/rcu/update.c | 7 +++++-- kernel/sched/fair.c | 2 +- 3 files changed, 7 insertions(+), 3 deletions(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 9be61e47badc..a225530b2ece 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -45,6 +45,7 @@ #include #include #include +#include #include diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c index 3e888cd5a594..f0d8322bc3ec 100644 --- a/kernel/rcu/update.c +++ b/kernel/rcu/update.c @@ -528,6 +528,7 @@ static int rcu_task_stall_timeout __read_mostly = HZ * 60 * 10; module_param(rcu_task_stall_timeout, int, 0644); static void rcu_spawn_tasks_kthread(void); +static struct task_struct *rcu_tasks_kthread_ptr; /* * Post an RCU-tasks callback. First call must be from process context @@ -537,6 +538,7 @@ void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func) { unsigned long flags; bool needwake; + bool havetask = READ_ONCE(rcu_tasks_kthread_ptr); rhp->next = NULL; rhp->func = func; @@ -545,7 +547,9 @@ void call_rcu_tasks(struct rcu_head *rhp, rcu_callback_t func) *rcu_tasks_cbs_tail = rhp; rcu_tasks_cbs_tail = &rhp->next; raw_spin_unlock_irqrestore(&rcu_tasks_cbs_lock, flags); - if (needwake) { + /* We can't create the thread unless interrupts are enabled. */ + if ((needwake && havetask) || + (!havetask && !irqs_disabled_flags(flags))) { rcu_spawn_tasks_kthread(); wake_up(&rcu_tasks_cbs_wq); } @@ -790,7 +794,6 @@ static int __noreturn rcu_tasks_kthread(void *arg) static void rcu_spawn_tasks_kthread(void) { static DEFINE_MUTEX(rcu_tasks_kthread_mutex); - static struct task_struct *rcu_tasks_kthread_ptr; struct task_struct *t; if (READ_ONCE(rcu_tasks_kthread_ptr)) { diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 218f8e83db73..4a3b279beb42 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -2175,7 +2175,7 @@ void task_numa_free(struct task_struct *p) grp->nr_tasks--; spin_unlock_irqrestore(&grp->lock, flags); - RCU_INIT_POINTER(p->numa_group, NULL); + rcu_assign_pointer(p->numa_group, NULL); put_numa_group(grp); } -- 2.5.2