Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932622AbbFGRtI (ORCPT ); Sun, 7 Jun 2015 13:49:08 -0400 Received: from terminus.zytor.com ([198.137.202.10]:57680 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932586AbbFGRtC (ORCPT ); Sun, 7 Jun 2015 13:49:02 -0400 Date: Sun, 7 Jun 2015 10:46:24 -0700 From: tip-bot for Frederic Weisbecker Message-ID: Cc: akpm@linux-foundation.org, torvalds@linux-foundation.org, rostedt@goodmis.org, peterz@infradead.org, linux-kernel@vger.kernel.org, fweisbec@gmail.com, hpa@zytor.com, mingo@kernel.org, fengguang.wu@intel.com, tglx@linutronix.de Reply-To: fengguang.wu@intel.com, mingo@kernel.org, hpa@zytor.com, tglx@linutronix.de, fweisbec@gmail.com, peterz@infradead.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org, torvalds@linux-foundation.org, rostedt@goodmis.org In-Reply-To: <1433432349-1021-2-git-send-email-fweisbec@gmail.com> References: <1433432349-1021-2-git-send-email-fweisbec@gmail.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:sched/core] sched: Make preempt_schedule_context() function-tracing safe Git-Commit-ID: be690035df893385ceaac2323b29be1fb7f2a67f 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 Content-Length: 3612 Lines: 87 Commit-ID: be690035df893385ceaac2323b29be1fb7f2a67f Gitweb: http://git.kernel.org/tip/be690035df893385ceaac2323b29be1fb7f2a67f Author: Frederic Weisbecker AuthorDate: Thu, 4 Jun 2015 17:39:07 +0200 Committer: Ingo Molnar CommitDate: Sun, 7 Jun 2015 15:57:41 +0200 sched: Make preempt_schedule_context() function-tracing safe Since function tracing disables preemption, it needs a safe preemption point to use when preemption is re-enabled without worrying about tracing recursion. Ie: to avoid tracing recursion, that preemption point can't be traced (use of notrace qualifier) and it can't call any traceable function before that preemption point disables preemption itself, which disarms the recursion. preempt_schedule() was fine until commit: b30f0e3ffedf ("sched/preempt: Optimize preemption operations on __schedule() callers") because PREEMPT_ACTIVE (which has the property to disable preemption and this disarm tracing preemption recursion) was set before calling any further function. But that commit introduced the use of preempt_count_add/sub() functions to set PREEMPT_ACTIVE and because these functions are called before preemption gets a chance to be disabled, we have a tracing recursion. preempt_schedule_context() is one of the possible preemption functions used by tracing. Its special purpose is to avoid tracing recursion against context tracking. Lets enhance this function to become more generally tracing safe by disabling preemption with raw accessors, such that no function is called before preemption gets disabled and disarm the tracing recursion. This function is going to become the specific tracing-safe preemption point in further commit. Reported-by: Fengguang Wu Signed-off-by: Frederic Weisbecker Signed-off-by: Peter Zijlstra (Intel) Cc: Andrew Morton Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Thomas Gleixner Link: http://lkml.kernel.org/r/1433432349-1021-2-git-send-email-fweisbec@gmail.com Signed-off-by: Ingo Molnar --- kernel/sched/core.c | 11 +++++++++-- 1 file changed, 9 insertions(+), 2 deletions(-) diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 20b858f..4e925ea 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2960,7 +2960,13 @@ asmlinkage __visible void __sched notrace preempt_schedule_context(void) return; do { - preempt_active_enter(); + /* + * Use raw __prempt_count() ops that don't call function. + * We can't call functions before disabling preemption which + * disarm preemption tracing recursions. + */ + __preempt_count_add(PREEMPT_ACTIVE + PREEMPT_DISABLE_OFFSET); + barrier(); /* * Needs preempt disabled in case user_exit() is traced * and the tracer calls preempt_enable_notrace() causing @@ -2970,7 +2976,8 @@ asmlinkage __visible void __sched notrace preempt_schedule_context(void) __schedule(); exception_exit(prev_ctx); - preempt_active_exit(); + barrier(); + __preempt_count_sub(PREEMPT_ACTIVE + PREEMPT_DISABLE_OFFSET); } while (need_resched()); } EXPORT_SYMBOL_GPL(preempt_schedule_context); -- 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/