From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: From: Kamal Mostafa To: linux-kernel@vger.kernel.org, stable@vger.kernel.org, kernel-team@lists.ubuntu.com Cc: Sebastian Andrzej Siewior , "Peter Zijlstra (Intel)" , Davidlohr Bueso , Linus Torvalds , Steven Rostedt , Thomas Gleixner , Ingo Molnar , Kamal Mostafa Subject: [PATCH 4.2.y-ckt 304/305] sched/core: Reset task's lockless wake-queues on fork() Date: Fri, 15 Jan 2016 16:01:58 -0800 Message-Id: <1452902519-2754-305-git-send-email-kamal@canonical.com> In-Reply-To: <1452902519-2754-1-git-send-email-kamal@canonical.com> References: <1452902519-2754-1-git-send-email-kamal@canonical.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: 4.2.8-ckt2 -stable review patch. If anyone has any objections, please let me know. ---8<------------------------------------------------------------ From: Sebastian Andrzej Siewior commit 093e5840ae76f1082633503964d035f40ed0216d upstream. In the following commit: 7675104990ed ("sched: Implement lockless wake-queues") we gained lockless wake-queues. The -RT kernel managed to lockup itself with those. There could be multiple attempts for task X to enqueue it for a wakeup _even_ if task X is already running. The reason is that task X could be runnable but not yet on CPU. The the task performing the wakeup did not leave the CPU it could performe multiple wakeups. With the proper timming task X could be running and enqueued for a wakeup. If this happens while X is performing a fork() then its its child will have a !NULL `wake_q` member copied. This is not a problem as long as the child task does not participate in lockless wakeups :) Signed-off-by: Sebastian Andrzej Siewior Signed-off-by: Peter Zijlstra (Intel) Cc: Davidlohr Bueso Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Thomas Gleixner Fixes: 7675104990ed ("sched: Implement lockless wake-queues") Link: http://lkml.kernel.org/r/20151221171710.GA5499@linutronix.de Signed-off-by: Ingo Molnar Signed-off-by: Kamal Mostafa --- kernel/fork.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/fork.c b/kernel/fork.c index e769c8c..a0fb0ce 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -379,6 +379,7 @@ static struct task_struct *dup_task_struct(struct task_struct *orig) #endif tsk->splice_pipe = NULL; tsk->task_frag.page = NULL; + tsk->wake_q.next = NULL; account_kernel_stack(ti, 1); -- 1.9.1