Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755200AbcCTIn5 (ORCPT ); Sun, 20 Mar 2016 04:43:57 -0400 Received: from mail-wm0-f67.google.com ([74.125.82.67]:36812 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751550AbcCTInt (ORCPT ); Sun, 20 Mar 2016 04:43:49 -0400 Message-ID: <1458463425.3908.5.camel@gmail.com> Subject: Re: [PATCH RT 4/6] rt/locking: Reenable migration accross schedule From: Mike Galbraith To: Sebastian Andrzej Siewior , linux-rt-users@vger.kernel.org Cc: linux-kernel@vger.kernel.org, tglx@linutronix.de, Steven Rostedt Date: Sun, 20 Mar 2016 09:43:45 +0100 In-Reply-To: <1455318168-7125-4-git-send-email-bigeasy@linutronix.de> References: <1455318168-7125-1-git-send-email-bigeasy@linutronix.de> <1455318168-7125-4-git-send-email-bigeasy@linutronix.de> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.16.5 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2474 Lines: 72 On Sat, 2016-02-13 at 00:02 +0100, Sebastian Andrzej Siewior wrote: > From: Thomas Gleixner > > We currently disable migration across lock acquisition. That includes the part > where we block on the lock and schedule out. We cannot disable migration after > taking the lock as that would cause a possible lock inversion. > > But we can be smart and enable migration when we block and schedule out. That > allows the scheduler to place the task freely at least if this is the first > migrate disable level. For nested locking this does not help at all. I met a problem while testing shiny new hotplug machinery. rt/locking: Fix rt_spin_lock_slowlock() vs hotplug migrate_disable() bug migrate_disable() -> pin_current_cpu() -> hotplug_lock() leads to.. BUG_ON(rt_mutex_real_waiter(task->pi_blocked_on)); ..so let's call migrate_disable() after we acquire the lock instead. Fixes: e24b142cfb4a rt/locking: Reenable migration accross schedule Signed-off-by: Mike Galbraith --- kernel/locking/rtmutex.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) --- a/kernel/locking/rtmutex.c +++ b/kernel/locking/rtmutex.c @@ -1011,7 +1011,7 @@ static void noinline __sched rt_spin_lo struct task_struct *lock_owner, *self = current; struct rt_mutex_waiter waiter, *top_waiter; unsigned long flags; - int ret; + bool mg_disable = false; rt_mutex_init_waiter(&waiter, true); @@ -1035,8 +1035,7 @@ static void noinline __sched rt_spin_lo __set_current_state_no_track(TASK_UNINTERRUPTIBLE); raw_spin_unlock(&self->pi_lock); - ret = task_blocks_on_rt_mutex(lock, &waiter, self, RT_MUTEX_MIN_CHAINWALK); - BUG_ON(ret); + BUG_ON(task_blocks_on_rt_mutex(lock, &waiter, self, RT_MUTEX_MIN_CHAINWALK)); for (;;) { /* Try to acquire the lock again. */ @@ -1051,11 +1050,12 @@ static void noinline __sched rt_spin_lo debug_rt_mutex_print_deadlock(&waiter); if (top_waiter != &waiter || adaptive_wait(lock, lock_owner)) { - if (mg_off) + if (mg_off && self->migrate_disable == 1) { + mg_off = false; + mg_disable = true; migrate_enable(); + } schedule(); - if (mg_off) - migrate_disable(); } raw_spin_lock_irqsave(&lock->wait_lock, flags); @@ -1088,6 +1088,9 @@ static void noinline __sched rt_spin_lo raw_spin_unlock_irqrestore(&lock->wait_lock, flags); + if (mg_disable) + migrate_disable(); + debug_rt_mutex_free_waiter(&waiter); }