From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752893AbdDFCMi (ORCPT ); Wed, 5 Apr 2017 22:12:38 -0400 Received: from mail.kernel.org ([198.145.29.136]:51166 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751169AbdDFCM2 (ORCPT ); Wed, 5 Apr 2017 22:12:28 -0400 Date: Wed, 5 Apr 2017 22:12:24 -0400 From: Steven Rostedt To: "Paul E. McKenney" Cc: LKML Subject: Re: [BUG] stack tracing causes: kernel/module.c:271 module_assert_mutex_or_preempt Message-ID: <20170405221224.0d265a3d@gandalf.local.home> In-Reply-To: <20170405175925.GG1600@linux.vnet.ibm.com> References: <20170405093207.404f8deb@gandalf.local.home> <20170405162515.GF1600@linux.vnet.ibm.com> <20170405124539.730a2365@gandalf.local.home> <20170405175925.GG1600@linux.vnet.ibm.com> X-Mailer: Claws Mail 3.14.0 (GTK+ 2.24.31; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 5 Apr 2017 10:59:25 -0700 "Paul E. McKenney" wrote: > > > Could you please let me know if tracing happens in NMI handlers? > > > If so, a bit of additional code will be needed. > > > > > > Thanx, Paul > > > > > > PS. Which reminds me, any short-term uses of RCU_TASKS? This represents > > > 3 of my 16 test scenarios, which is getting hard to justify for > > > something that isn't used. Especially given that I will need to > > > add more scenarios for parallel-callbacks SRCU... > > > > The RCU_TASK implementation is next on my todo list. Yes, there's going > > to be plenty of users very soon. Not for 4.12 but definitely for 4.13. > > > > Sorry for the delay in implementing that :-/ > > OK, I will wait a few months before checking again... > Actually, I took a quick look at what needs to be done, and I think it is *really* easy, and may be available in 4.12! Here's the current patch. I can probably do a patch to allow optimized kprobes on PREEMPT kernels as well. -- Steve diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c index 8efd9fe..28e3019 100644 --- a/kernel/trace/ftrace.c +++ b/kernel/trace/ftrace.c @@ -2808,18 +2808,28 @@ static int ftrace_shutdown(struct ftrace_ops *ops, int command) * callers are done before leaving this function. * The same goes for freeing the per_cpu data of the per_cpu * ops. - * - * Again, normal synchronize_sched() is not good enough. - * We need to do a hard force of sched synchronization. - * This is because we use preempt_disable() to do RCU, but - * the function tracers can be called where RCU is not watching - * (like before user_exit()). We can not rely on the RCU - * infrastructure to do the synchronization, thus we must do it - * ourselves. */ if (ops->flags & (FTRACE_OPS_FL_DYNAMIC | FTRACE_OPS_FL_PER_CPU)) { + /* + * We need to do a hard force of sched synchronization. + * This is because we use preempt_disable() to do RCU, but + * the function tracers can be called where RCU is not watching + * (like before user_exit()). We can not rely on the RCU + * infrastructure to do the synchronization, thus we must do it + * ourselves. + */ schedule_on_each_cpu(ftrace_sync); +#ifdef CONFIG_PREEMPT + /* + * When the kernel is preeptive, tasks can be preempted + * while on a ftrace trampoline. Just scheduling a task on + * a CPU is not good enough to flush them. Calling + * synchronize_rcu_tasks() will wait for those tasks to + * execute and either schedule voluntarily or enter user space. + */ + synchronize_rcu_tasks(); +#endif arch_ftrace_trampoline_free(ops); if (ops->flags & FTRACE_OPS_FL_PER_CPU) @@ -5366,22 +5376,6 @@ void __weak arch_ftrace_update_trampoline(struct ftrace_ops *ops) static void ftrace_update_trampoline(struct ftrace_ops *ops) { - -/* - * Currently there's no safe way to free a trampoline when the kernel - * is configured with PREEMPT. That is because a task could be preempted - * when it jumped to the trampoline, it may be preempted for a long time - * depending on the system load, and currently there's no way to know - * when it will be off the trampoline. If the trampoline is freed - * too early, when the task runs again, it will be executing on freed - * memory and crash. - */ -#ifdef CONFIG_PREEMPT - /* Currently, only non dynamic ops can have a trampoline */ - if (ops->flags & FTRACE_OPS_FL_DYNAMIC) - return; -#endif - arch_ftrace_update_trampoline(ops); }