From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752405AbdEUKX0 (ORCPT ); Sun, 21 May 2017 06:23:26 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:33856 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750824AbdEUKXZ (ORCPT ); Sun, 21 May 2017 06:23:25 -0400 Date: Sun, 21 May 2017 12:23:22 +0200 (CEST) From: Thomas Gleixner To: Linus Torvalds cc: LKML , Andrew Morton , Ingo Molnar , "H. Peter Anvin" Subject: [GIT pull] scheduler fix for 4.12 Message-ID: User-Agent: Alpine 2.20 (DEB 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Linus, please pull the latest sched-urgent-for-linus git tree from: git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git sched-urgent-for-linus A single scheduler fix: Prevent idle task from ever being preempted. That makes sure that synchronize_rcu_tasks() which is ignoring idle task does not pretend that no task is stuck in preempted state. If that happens and idle was preempted on a ftrace trampoline the machine crashes due to inconsistent state. Thanks, tglx ------------------> Steven Rostedt (VMware) (1): sched/core: Call __schedule() from do_idle() without enabling preemption kernel/sched/core.c | 25 +++++++++++++++++++++++++ kernel/sched/idle.c | 2 +- kernel/sched/sched.h | 2 ++ 3 files changed, 28 insertions(+), 1 deletion(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 759f4bd52cd6..803c3bc274c4 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -3502,6 +3502,31 @@ asmlinkage __visible void __sched schedule(void) } EXPORT_SYMBOL(schedule); +/* + * synchronize_rcu_tasks() makes sure that no task is stuck in preempted + * state (have scheduled out non-voluntarily) by making sure that all + * tasks have either left the run queue or have gone into user space. + * As idle tasks do not do either, they must not ever be preempted + * (schedule out non-voluntarily). + * + * schedule_idle() is similar to schedule_preempt_disable() except that it + * never enables preemption because it does not call sched_submit_work(). + */ +void __sched schedule_idle(void) +{ + /* + * As this skips calling sched_submit_work(), which the idle task does + * regardless because that function is a nop when the task is in a + * TASK_RUNNING state, make sure this isn't used someplace that the + * current task can be in any other state. Note, idle is always in the + * TASK_RUNNING state. + */ + WARN_ON_ONCE(current->state); + do { + __schedule(false); + } while (need_resched()); +} + #ifdef CONFIG_CONTEXT_TRACKING asmlinkage __visible void __sched schedule_user(void) { diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c index 2a25a9ec2c6e..ef63adce0c9c 100644 --- a/kernel/sched/idle.c +++ b/kernel/sched/idle.c @@ -265,7 +265,7 @@ static void do_idle(void) smp_mb__after_atomic(); sched_ttwu_pending(); - schedule_preempt_disabled(); + schedule_idle(); if (unlikely(klp_patch_pending(current))) klp_update_patch_state(current); diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 7808ab050599..6dda2aab731e 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1467,6 +1467,8 @@ static inline struct cpuidle_state *idle_get_state(struct rq *rq) } #endif +extern void schedule_idle(void); + extern void sysrq_sched_debug_show(void); extern void sched_init_granularity(void); extern void update_max_interval(void);