From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934612AbbI2JpQ (ORCPT ); Tue, 29 Sep 2015 05:45:16 -0400 Received: from bombadil.infradead.org ([198.137.202.9]:60748 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934325AbbI2JnQ (ORCPT ); Tue, 29 Sep 2015 05:43:16 -0400 Message-Id: <20150929093519.817299442@infradead.org> User-Agent: quilt/0.61-1 Date: Tue, 29 Sep 2015 11:28:27 +0200 From: Peter Zijlstra To: mingo@kernel.org Cc: linux-kernel@vger.kernel.org, torvalds@linux-foundation.org, fweisbec@gmail.com, oleg@redhat.com, umgwanakikbuti@gmail.com, tglx@linutronix.de, rostedt@goodmis.org, Peter Zijlstra Subject: [RFC][PATCH 02/11] sched: Create preempt_count invariant References: <20150929092825.540553633@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline; filename=peterz-kill-preempt_active-2.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Ensure that upon scheduling preempt_count == 2; although currently an additional PREEMPT_ACTIVE is still possible. Signed-off-by: Peter Zijlstra (Intel) --- arch/x86/include/asm/preempt.h | 3 ++- include/asm-generic/preempt.h | 2 +- kernel/sched/core.c | 14 ++++++++++---- 3 files changed, 13 insertions(+), 6 deletions(-) --- a/arch/x86/include/asm/preempt.h +++ b/arch/x86/include/asm/preempt.h @@ -31,7 +31,8 @@ static __always_inline void preempt_coun * must be macros to avoid header recursion hell */ #define init_task_preempt_count(p) do { \ - task_thread_info(p)->saved_preempt_count = PREEMPT_DISABLED; \ + task_thread_info(p)->saved_preempt_count = \ + 2*PREEMPT_DISABLE_OFFSET + PREEMPT_NEED_RESCHED; \ } while (0) #define init_idle_preempt_count(p, cpu) do { \ --- a/include/asm-generic/preempt.h +++ b/include/asm-generic/preempt.h @@ -24,7 +24,7 @@ static __always_inline void preempt_coun * must be macros to avoid header recursion hell */ #define init_task_preempt_count(p) do { \ - task_thread_info(p)->preempt_count = PREEMPT_DISABLED; \ + task_thread_info(p)->preempt_count = 2*PREEMPT_DISABLED; \ } while (0) #define init_idle_preempt_count(p, cpu) do { \ --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2588,11 +2588,17 @@ asmlinkage __visible void schedule_tail( { struct rq *rq; - /* finish_task_switch() drops rq->lock and enables preemtion */ - preempt_disable(); - rq = finish_task_switch(prev); + /* + * Still have preempt_count() == 2, from: + * + * schedule() + * preempt_disable(); // 1 + * __schedule() + * raw_spin_lock_irq(&rq->lock) // 2 + */ + rq = finish_task_switch(prev); /* drops rq->lock, preempt_count() == 1 */ balance_callback(rq); - preempt_enable(); + preempt_enable(); /* preempt_count() == 0 */ if (current->set_child_tid) put_user(task_pid_vnr(current), current->set_child_tid);