From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: Re: [PATCH v3 08/22] rcu,tracing: Create trace_rcu_{enter,exit}() Date: Thu, 20 Feb 2020 05:58:00 -0800 Message-ID: <20200220135800.GT2935@paulmck-ThinkPad-P72> References: <20200219144724.800607165@infradead.org> <20200219150744.832297480@infradead.org> <20200219104903.46686b81@gandalf.local.home> <20200219155828.GF18400@hirez.programming.kicks-ass.net> <20200219111532.719c0a6b@gandalf.local.home> <20200219163535.GJ18400@hirez.programming.kicks-ass.net> <20200219164449.GC2935@paulmck-ThinkPad-P72> <20200220103421.GV18400@hirez.programming.kicks-ass.net> Reply-To: paulmck@kernel.org Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20200220103421.GV18400@hirez.programming.kicks-ass.net> Sender: linux-kernel-owner@vger.kernel.org To: Peter Zijlstra Cc: Steven Rostedt , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, mingo@kernel.org, joel@joelfernandes.org, gregkh@linuxfoundation.org, gustavo@embeddedor.com, tglx@linutronix.de, josh@joshtriplett.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, luto@kernel.org, tony.luck@intel.com, frederic@kernel.org, dan.carpenter@oracle.com, mhiramat@kernel.org List-Id: linux-arch.vger.kernel.org On Thu, Feb 20, 2020 at 11:34:21AM +0100, Peter Zijlstra wrote: > On Wed, Feb 19, 2020 at 08:44:50AM -0800, Paul E. McKenney wrote: > > On Wed, Feb 19, 2020 at 05:35:35PM +0100, Peter Zijlstra wrote: > > > > Possibly, and I suppose the current version is less obviously dependent > > > on the in_nmi() functionality as was the previous, seeing how Paul > > > frobbed that all the way into the rcu_irq_enter*() implementation. > > > > > > So sure, I can go move it I suppose. > > > > No objections here. > > It now looks like so: > > --- > Subject: rcu,tracing: Create trace_rcu_{enter,exit}() > From: Peter Zijlstra > Date: Wed Feb 12 09:18:57 CET 2020 > > To facilitate tracers that need RCU, add some helpers to wrap the > magic required. > > The problem is that we can call into tracers (trace events and > function tracing) while RCU isn't watching and this can happen from > any context, including NMI. > > Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Paul E. McKenney > --- > include/linux/rcupdate.h | 29 +++++++++++++++++++++++++++++ > 1 file changed, 29 insertions(+) > > --- a/include/linux/rcupdate.h > +++ b/include/linux/rcupdate.h > @@ -175,6 +175,35 @@ do { \ > #error "Unknown RCU implementation specified to kernel configuration" > #endif > > +/** > + * trace_rcu_enter - Force RCU to be active, for code that needs RCU readers > + * > + * Very similar to RCU_NONIDLE() above. > + * > + * Tracing can happen while RCU isn't active yet, for instance in the idle loop > + * between rcu_idle_enter() and rcu_idle_exit(), or early in exception entry. > + * RCU will happily ignore any read-side critical sections in this case. > + * > + * This function ensures that RCU is aware hereafter and the code can readily > + * rely on RCU read-side critical sections working as expected. > + * > + * This function is NMI safe -- provided in_nmi() is correct and will nest up-to > + * INT_MAX/2 times. > + */ > +static inline int trace_rcu_enter(void) > +{ > + int state = !rcu_is_watching(); > + if (state) > + rcu_irq_enter_irqsave(); > + return state; > +} > + > +static inline void trace_rcu_exit(int state) > +{ > + if (state) > + rcu_irq_exit_irqsave(); > +} > + > /* > * The init_rcu_head_on_stack() and destroy_rcu_head_on_stack() calls > * are needed for dynamic initialization and destruction of rcu_head From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org ([198.145.29.99]:38830 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727943AbgBTN6C (ORCPT ); Thu, 20 Feb 2020 08:58:02 -0500 Date: Thu, 20 Feb 2020 05:58:00 -0800 From: "Paul E. McKenney" Subject: Re: [PATCH v3 08/22] rcu,tracing: Create trace_rcu_{enter,exit}() Message-ID: <20200220135800.GT2935@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200219144724.800607165@infradead.org> <20200219150744.832297480@infradead.org> <20200219104903.46686b81@gandalf.local.home> <20200219155828.GF18400@hirez.programming.kicks-ass.net> <20200219111532.719c0a6b@gandalf.local.home> <20200219163535.GJ18400@hirez.programming.kicks-ass.net> <20200219164449.GC2935@paulmck-ThinkPad-P72> <20200220103421.GV18400@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200220103421.GV18400@hirez.programming.kicks-ass.net> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Peter Zijlstra Cc: Steven Rostedt , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, mingo@kernel.org, joel@joelfernandes.org, gregkh@linuxfoundation.org, gustavo@embeddedor.com, tglx@linutronix.de, josh@joshtriplett.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, luto@kernel.org, tony.luck@intel.com, frederic@kernel.org, dan.carpenter@oracle.com, mhiramat@kernel.org Message-ID: <20200220135800.7P3LjzC4pVRsFLVh1mMN8hcfi266xUSLXY6RkFV8SaY@z> On Thu, Feb 20, 2020 at 11:34:21AM +0100, Peter Zijlstra wrote: > On Wed, Feb 19, 2020 at 08:44:50AM -0800, Paul E. McKenney wrote: > > On Wed, Feb 19, 2020 at 05:35:35PM +0100, Peter Zijlstra wrote: > > > > Possibly, and I suppose the current version is less obviously dependent > > > on the in_nmi() functionality as was the previous, seeing how Paul > > > frobbed that all the way into the rcu_irq_enter*() implementation. > > > > > > So sure, I can go move it I suppose. > > > > No objections here. > > It now looks like so: > > --- > Subject: rcu,tracing: Create trace_rcu_{enter,exit}() > From: Peter Zijlstra > Date: Wed Feb 12 09:18:57 CET 2020 > > To facilitate tracers that need RCU, add some helpers to wrap the > magic required. > > The problem is that we can call into tracers (trace events and > function tracing) while RCU isn't watching and this can happen from > any context, including NMI. > > Signed-off-by: Peter Zijlstra (Intel) Reviewed-by: Paul E. McKenney > --- > include/linux/rcupdate.h | 29 +++++++++++++++++++++++++++++ > 1 file changed, 29 insertions(+) > > --- a/include/linux/rcupdate.h > +++ b/include/linux/rcupdate.h > @@ -175,6 +175,35 @@ do { \ > #error "Unknown RCU implementation specified to kernel configuration" > #endif > > +/** > + * trace_rcu_enter - Force RCU to be active, for code that needs RCU readers > + * > + * Very similar to RCU_NONIDLE() above. > + * > + * Tracing can happen while RCU isn't active yet, for instance in the idle loop > + * between rcu_idle_enter() and rcu_idle_exit(), or early in exception entry. > + * RCU will happily ignore any read-side critical sections in this case. > + * > + * This function ensures that RCU is aware hereafter and the code can readily > + * rely on RCU read-side critical sections working as expected. > + * > + * This function is NMI safe -- provided in_nmi() is correct and will nest up-to > + * INT_MAX/2 times. > + */ > +static inline int trace_rcu_enter(void) > +{ > + int state = !rcu_is_watching(); > + if (state) > + rcu_irq_enter_irqsave(); > + return state; > +} > + > +static inline void trace_rcu_exit(int state) > +{ > + if (state) > + rcu_irq_exit_irqsave(); > +} > + > /* > * The init_rcu_head_on_stack() and destroy_rcu_head_on_stack() calls > * are needed for dynamic initialization and destruction of rcu_head