Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755520AbaJ1LEd (ORCPT ); Tue, 28 Oct 2014 07:04:33 -0400 Received: from terminus.zytor.com ([198.137.202.10]:50959 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755335AbaJ1LE2 (ORCPT ); Tue, 28 Oct 2014 07:04:28 -0400 Date: Tue, 28 Oct 2014 04:03:13 -0700 From: tip-bot for Oleg Nesterov Message-ID: Cc: hpa@zytor.com, torvalds@linux-foundation.org, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, cebbert.lkml@gmail.com, fweisbec@gmail.com, oleg@redhat.com, dvlasenk@redhat.com, mingo@kernel.org, sasha.levin@oracle.com, masami.hiramatsu.pt@hitachi.com, agraf@suse.de, luto@amacapital.net, peterz@infradead.org, cl@linux.com, tglx@linutronix.de, rostedt@goodmis.org Reply-To: agraf@suse.de, masami.hiramatsu.pt@hitachi.com, luto@amacapital.net, peterz@infradead.org, tglx@linutronix.de, cl@linux.com, rostedt@goodmis.org, hpa@zytor.com, linux-kernel@vger.kernel.org, cebbert.lkml@gmail.com, torvalds@linux-foundation.org, akpm@linux-foundation.org, oleg@redhat.com, fweisbec@gmail.com, mingo@kernel.org, sasha.levin@oracle.com, dvlasenk@redhat.com In-Reply-To: <20141005202322.GB27962@redhat.com> References: <20141005202322.GB27962@redhat.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:sched/core] sched: stop the unbound recursion in preempt_schedule_context() Git-Commit-ID: 009f60e2763568cdcd75bd1cf360c7c7165e2e60 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: 009f60e2763568cdcd75bd1cf360c7c7165e2e60 Gitweb: http://git.kernel.org/tip/009f60e2763568cdcd75bd1cf360c7c7165e2e60 Author: Oleg Nesterov AuthorDate: Sun, 5 Oct 2014 22:23:22 +0200 Committer: Ingo Molnar CommitDate: Tue, 28 Oct 2014 10:46:05 +0100 sched: stop the unbound recursion in preempt_schedule_context() preempt_schedule_context() does preempt_enable_notrace() at the end and this can call the same function again; exception_exit() is heavy and it is quite possible that need-resched is true again. 1. Change this code to dec preempt_count() and check need_resched() by hand. 2. As Linus suggested, we can use the PREEMPT_ACTIVE bit and avoid the enable/disable dance around __schedule(). But in this case we need to move into sched/core.c. 3. Cosmetic, but x86 forgets to declare this function. This doesn't really matter because it is only called by asm helpers, still it make sense to add the declaration into asm/preempt.h to match preempt_schedule(). Reported-by: Sasha Levin Signed-off-by: Oleg Nesterov Signed-off-by: Peter Zijlstra (Intel) Cc: Alexander Graf Cc: Andrew Morton Cc: Christoph Lameter Cc: Linus Torvalds Cc: Masami Hiramatsu Cc: Steven Rostedt Cc: Peter Anvin Cc: Andy Lutomirski Cc: Denys Vlasenko Cc: Chuck Ebbert Cc: Frederic Weisbecker Link: http://lkml.kernel.org/r/20141005202322.GB27962@redhat.com Signed-off-by: Ingo Molnar --- arch/x86/include/asm/preempt.h | 1 + kernel/context_tracking.c | 40 ---------------------------------------- kernel/sched/core.c | 41 +++++++++++++++++++++++++++++++++++++++++ 3 files changed, 42 insertions(+), 40 deletions(-) diff --git a/arch/x86/include/asm/preempt.h b/arch/x86/include/asm/preempt.h index 7024c12..4008734 100644 --- a/arch/x86/include/asm/preempt.h +++ b/arch/x86/include/asm/preempt.h @@ -105,6 +105,7 @@ static __always_inline bool should_resched(void) # ifdef CONFIG_CONTEXT_TRACKING extern asmlinkage void ___preempt_schedule_context(void); # define __preempt_schedule_context() asm ("call ___preempt_schedule_context") + extern asmlinkage void preempt_schedule_context(void); # endif #endif diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c index 5664985..937ecdf 100644 --- a/kernel/context_tracking.c +++ b/kernel/context_tracking.c @@ -107,46 +107,6 @@ void context_tracking_user_enter(void) } NOKPROBE_SYMBOL(context_tracking_user_enter); -#ifdef CONFIG_PREEMPT -/** - * preempt_schedule_context - preempt_schedule called by tracing - * - * The tracing infrastructure uses preempt_enable_notrace to prevent - * recursion and tracing preempt enabling caused by the tracing - * infrastructure itself. But as tracing can happen in areas coming - * from userspace or just about to enter userspace, a preempt enable - * can occur before user_exit() is called. This will cause the scheduler - * to be called when the system is still in usermode. - * - * To prevent this, the preempt_enable_notrace will use this function - * instead of preempt_schedule() to exit user context if needed before - * calling the scheduler. - */ -asmlinkage __visible void __sched notrace preempt_schedule_context(void) -{ - enum ctx_state prev_ctx; - - if (likely(!preemptible())) - return; - - /* - * Need to disable preemption in case user_exit() is traced - * and the tracer calls preempt_enable_notrace() causing - * an infinite recursion. - */ - preempt_disable_notrace(); - prev_ctx = exception_enter(); - preempt_enable_no_resched_notrace(); - - preempt_schedule(); - - preempt_disable_notrace(); - exception_exit(prev_ctx); - preempt_enable_notrace(); -} -EXPORT_SYMBOL_GPL(preempt_schedule_context); -#endif /* CONFIG_PREEMPT */ - /** * context_tracking_user_exit - Inform the context tracking that the CPU is * exiting userspace mode and entering the kernel. diff --git a/kernel/sched/core.c b/kernel/sched/core.c index dde8adb..240157c 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2951,6 +2951,47 @@ asmlinkage __visible void __sched notrace preempt_schedule(void) } NOKPROBE_SYMBOL(preempt_schedule); EXPORT_SYMBOL(preempt_schedule); + +#ifdef CONFIG_CONTEXT_TRACKING +/** + * preempt_schedule_context - preempt_schedule called by tracing + * + * The tracing infrastructure uses preempt_enable_notrace to prevent + * recursion and tracing preempt enabling caused by the tracing + * infrastructure itself. But as tracing can happen in areas coming + * from userspace or just about to enter userspace, a preempt enable + * can occur before user_exit() is called. This will cause the scheduler + * to be called when the system is still in usermode. + * + * To prevent this, the preempt_enable_notrace will use this function + * instead of preempt_schedule() to exit user context if needed before + * calling the scheduler. + */ +asmlinkage __visible void __sched notrace preempt_schedule_context(void) +{ + enum ctx_state prev_ctx; + + if (likely(!preemptible())) + return; + + do { + __preempt_count_add(PREEMPT_ACTIVE); + /* + * Needs preempt disabled in case user_exit() is traced + * and the tracer calls preempt_enable_notrace() causing + * an infinite recursion. + */ + prev_ctx = exception_enter(); + __schedule(); + exception_exit(prev_ctx); + + __preempt_count_sub(PREEMPT_ACTIVE); + barrier(); + } while (need_resched()); +} +EXPORT_SYMBOL_GPL(preempt_schedule_context); +#endif /* CONFIG_CONTEXT_TRACKING */ + #endif /* CONFIG_PREEMPT */ /* -- 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/