From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S966961AbdEWItq (ORCPT ); Tue, 23 May 2017 04:49:46 -0400 Received: from terminus.zytor.com ([65.50.211.136]:44577 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757350AbdEWIto (ORCPT ); Tue, 23 May 2017 04:49:44 -0400 Date: Tue, 23 May 2017 01:46:00 -0700 From: "tip-bot for Steven Rostedt (VMware)" Message-ID: Cc: rostedt@goodmis.org, ldufour@linux.vnet.ibm.com, hpa@zytor.com, peterz@infradead.org, torvalds@linux-foundation.org, mingo@kernel.org, tglx@linutronix.de, linux-kernel@vger.kernel.org, akpm@osdl.org Reply-To: tglx@linutronix.de, mingo@kernel.org, linux-kernel@vger.kernel.org, akpm@osdl.org, rostedt@goodmis.org, ldufour@linux.vnet.ibm.com, hpa@zytor.com, peterz@infradead.org, torvalds@linux-foundation.org In-Reply-To: <20170308124654.10e598f2@gandalf.local.home> References: <20170308124654.10e598f2@gandalf.local.home> To: linux-tip-commits@vger.kernel.org Subject: [tip:sched/core] sched/core: Allow __sched_setscheduler() in interrupts when PI is not used Git-Commit-ID: 896bbb2522587e3b8eb2a0d204d43ccc1042a00d X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 896bbb2522587e3b8eb2a0d204d43ccc1042a00d Gitweb: http://git.kernel.org/tip/896bbb2522587e3b8eb2a0d204d43ccc1042a00d Author: Steven Rostedt (VMware) AuthorDate: Thu, 9 Mar 2017 10:18:42 -0500 Committer: Ingo Molnar CommitDate: Tue, 23 May 2017 10:01:34 +0200 sched/core: Allow __sched_setscheduler() in interrupts when PI is not used When priority inheritance was added back in 2.6.18 to sched_setscheduler(), it added a path to taking an rt-mutex wait_lock, which is not IRQ safe. As PI is not a common occurrence, lockdep will likely never trigger if sched_setscheduler was called from interrupt context. A BUG_ON() was added to trigger if __sched_setscheduler() was ever called from interrupt context because there was a possibility to take the wait_lock. Today the wait_lock is irq safe, but the path to taking it in sched_setscheduler() is the same as the path to taking it from normal context. The wait_lock is taken with raw_spin_lock_irq() and released with raw_spin_unlock_irq() which will indiscriminately enable interrupts, which would be bad in interrupt context. The problem is that normalize_rt_tasks, which is called by triggering the sysrq nice-all-RT-tasks was changed to call __sched_setscheduler(), and this is done from interrupt context! Now __sched_setscheduler() takes a "pi" parameter that is used to know if the priority inheritance should be called or not. As the BUG_ON() only cares about calling the PI code, it should only bug if called from interrupt context with the "pi" parameter set to true. Reported-by: Laurent Dufour Tested-by: Laurent Dufour Signed-off-by: Steven Rostedt (VMware) Signed-off-by: Peter Zijlstra (Intel) Cc: Andrew Morton Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Fixes: dbc7f069b93a ("sched: Use replace normalize_task() with __sched_setscheduler()") Link: http://lkml.kernel.org/r/20170308124654.10e598f2@gandalf.local.home Signed-off-by: Ingo Molnar --- kernel/sched/core.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 4a31239..877241e 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -4188,8 +4188,8 @@ static int __sched_setscheduler(struct task_struct *p, int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK; struct rq *rq; - /* May grab non-irq protected spin_locks: */ - BUG_ON(in_interrupt()); + /* The pi code expects interrupts enabled */ + BUG_ON(pi && in_interrupt()); recheck: /* Double check policy once rq lock held: */ if (policy < 0) {