From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753419AbcJDIJL (ORCPT ); Tue, 4 Oct 2016 04:09:11 -0400 Received: from terminus.zytor.com ([198.137.202.10]:37214 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751647AbcJDIJJ (ORCPT ); Tue, 4 Oct 2016 04:09:09 -0400 Date: Tue, 4 Oct 2016 01:06:56 -0700 From: tip-bot for Ingo Molnar Message-ID: Cc: mingo@kernel.org, kernel@kolivas.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, peterz@infradead.org, xiaolong.ye@intel.com, cchalpha@gmail.com, hpa@zytor.com Reply-To: hpa@zytor.com, cchalpha@gmail.com, xiaolong.ye@intel.com, peterz@infradead.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, kernel@kolivas.org, mingo@kernel.org In-Reply-To: <20160930015102.GB20189@yexl-desktop> References: <20160930015102.GB20189@yexl-desktop> To: linux-tip-commits@vger.kernel.org Subject: [tip:sched/urgent] Revert "sched/core: Do not use smp_processor_id() with preempt enabled in smpboot_thread_fn()" Git-Commit-ID: be6a2e4c46cc122ba9113ba569fbc50fad075fff 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: be6a2e4c46cc122ba9113ba569fbc50fad075fff Gitweb: http://git.kernel.org/tip/be6a2e4c46cc122ba9113ba569fbc50fad075fff Author: Ingo Molnar AuthorDate: Tue, 4 Oct 2016 09:55:57 +0200 Committer: Ingo Molnar CommitDate: Tue, 4 Oct 2016 09:55:57 +0200 Revert "sched/core: Do not use smp_processor_id() with preempt enabled in smpboot_thread_fn()" This reverts commit 4fa5cd5245b627db88c9ca08ae442373b02596b4. The original change widens a preempt-off section, to avoid a seemingly unsafe smp_processor_id() use. During review I overlooked two facts: - The code to calls a non-trivial function callback: ht->park(td->cpu); ... which might (and does occasionally) sleep, triggering the warning. - More importantly, as pointed out by Peter Zijlstra, using smp_processor_id() in that context is safe, if it's done from a kernel thread that is pinned to a single CPU - which is the case here. So revert to the original code that enables preemption sooner. Reported-by: kernel test robot Acked-by: Peter Zijlstra Cc: Con Kolivas Cc: Alfred Chen Link: http://lkml.kernel.org/r/20160930015102.GB20189@yexl-desktop Signed-off-by: Ingo Molnar --- kernel/smpboot.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/kernel/smpboot.c b/kernel/smpboot.c index fc0d8270..13bc43d 100644 --- a/kernel/smpboot.c +++ b/kernel/smpboot.c @@ -122,12 +122,12 @@ static int smpboot_thread_fn(void *data) if (kthread_should_park()) { __set_current_state(TASK_RUNNING); + preempt_enable(); if (ht->park && td->status == HP_THREAD_ACTIVE) { BUG_ON(td->cpu != smp_processor_id()); ht->park(td->cpu); td->status = HP_THREAD_PARKED; } - preempt_enable(); kthread_parkme(); /* We might have been woken for stop */ continue;