Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752030AbaBMPvk (ORCPT ); Thu, 13 Feb 2014 10:51:40 -0500 Received: from relay.parallels.com ([195.214.232.42]:49894 "EHLO relay.parallels.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751606AbaBMPvj (ORCPT ); Thu, 13 Feb 2014 10:51:39 -0500 Message-ID: <1392306716.5384.3.camel@tkhai> Subject: [PATCH] sched/core: Create new task with twice disabled preemption From: Kirill Tkhai To: CC: Peter Zijlstra , Ingo Molnar , Date: Thu, 13 Feb 2014 19:51:56 +0400 Organization: Parallels Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.4.4-3 MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Originating-IP: [10.30.26.172] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Preemption state on enter in finish_task_switch() is different in cases of context_switch() and schedule_tail(). In the first case we have it twice disabled: at the start of schedule() and during spin locking. In the second it is only once: the value which was set in init_task_preempt_count(). For archs without __ARCH_WANT_UNLOCKED_CTXSW set this means that all newly created tasks execute finish_arch_post_lock_switch() and post_schedule() with preemption enabled. It seems there is possible a problem in rare situations on arm64, when one freshly created thread preempts another before finish_arch_post_lock_switch() has finished. If mm is the same, then TIF_SWITCH_MM on the second won't be set. The second rare but possible issue is zeroing of post_schedule() on a wrong cpu. So, lets fix this and unify preempt_count state. Signed-off-by: Kirill Tkhai CC: Peter Zijlstra CC: Ingo Molnar --- arch/x86/include/asm/preempt.h | 6 ++++-- include/asm-generic/preempt.h | 6 ++++-- include/linux/sched.h | 2 ++ kernel/sched/core.c | 6 ++---- 4 files changed, 12 insertions(+), 8 deletions(-) diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h index c8b0519..07fdf52 100644 --- a/arch/x86/include/asm/preempt.h +++ b/arch/x86/include/asm/preempt.h @@ -32,9 +32,11 @@ static __always_inline void preempt_count_set(int pc) */ #define task_preempt_count(p) \ (task_thread_info(p)->saved_preempt_count & ~PREEMPT_NEED_RESCHED) - +/* + * Disable it twice to enter schedule_tail() with preemption disabled. + */ #define init_task_preempt_count(p) do { \ - task_thread_info(p)->saved_preempt_count = PREEMPT_DISABLED; \ + task_thread_info(p)->saved_preempt_count = PREEMPT_DISABLED_TWICE; \ } while (0) #define init_idle_preempt_count(p, cpu) do { \ diff --git a/include/asm-generic/preempt.h b/include/asm-generic/preempt.h index 1cd3f5d..0f67846 100644 --- a/include/asm-generic/preempt.h +++ b/include/asm-generic/preempt.h @@ -25,9 +25,11 @@ static __always_inline void preempt_count_set(int pc) */ #define task_preempt_count(p) \ (task_thread_info(p)->preempt_count & ~PREEMPT_NEED_RESCHED) - +/* + * Disable it twice to enter schedule_tail() with preemption disabled. + */ #define init_task_preempt_count(p) do { \ - task_thread_info(p)->preempt_count = PREEMPT_DISABLED; \ + task_thread_info(p)->preempt_count = PREEMPT_DISABLED_TWICE; \ } while (0) #define init_idle_preempt_count(p, cpu) do { \ diff --git a/include/linux/sched.h b/include/linux/sched.h index c49a258..f6a6c1e 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -520,8 +520,10 @@ struct task_cputime { #ifdef CONFIG_PREEMPT_COUNT #define PREEMPT_DISABLED (1 + PREEMPT_ENABLED) +#define PREEMPT_DISABLED_TWICE (2 + PREEMPT_ENABLED) #else #define PREEMPT_DISABLED PREEMPT_ENABLED +#define PREEMPT_DISABLED_TWICE PREEMPT_ENABLED #endif /* diff --git a/kernel/sched/core.c b/kernel/sched/core.c index fb9764f..18aa7f2 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2203,12 +2203,10 @@ asmlinkage void schedule_tail(struct task_struct *prev) finish_task_switch(rq, prev); - /* - * FIXME: do we need to worry about rq being invalidated by the - * task_switch? - */ post_schedule(rq); + preempt_enable(); + #ifdef __ARCH_WANT_UNLOCKED_CTXSW /* In this case, finish_task_switch does not reenable preemption */ preempt_enable(); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/