From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH v2 3/9] rcu,tracing: Create trace_rcu_{enter,exit}() Date: Tue, 18 Feb 2020 20:58:31 +0100 Message-ID: <20200218195831.GD11457@worktop.programming.kicks-ass.net> References: <20200212210139.382424693@infradead.org> <20200212210749.971717428@infradead.org> <20200212232005.GC115917@google.com> <20200213082716.GI14897@hirez.programming.kicks-ass.net> <20200213135138.GB2935@paulmck-ThinkPad-P72> <20200213164031.GH14914@hirez.programming.kicks-ass.net> <20200213185612.GG2935@paulmck-ThinkPad-P72> <20200213204444.GA94647@google.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20200213204444.GA94647@google.com> Sender: linux-kernel-owner@vger.kernel.org To: Joel Fernandes Cc: "Paul E. McKenney" , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, rostedt@goodmis.org, mingo@kernel.org, gregkh@linuxfoundation.org, gustavo@embeddedor.com, tglx@linutronix.de, josh@joshtriplett.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com List-Id: linux-arch.vger.kernel.org On Thu, Feb 13, 2020 at 03:44:44PM -0500, Joel Fernandes wrote: > > > That _should_ already be the case today. That is, if we end up in a > > > tracer and in_nmi() is unreliable we're already screwed anyway. > I removed the static from rcu_nmi_enter()/exit() as it is called from > outside, that makes it build now. Updated below is Paul's diff. I also added > NOKPROBE_SYMBOL() to rcu_nmi_exit() to match rcu_nmi_enter() since it seemed > asymmetric. > +__always_inline void rcu_nmi_exit(void) > { > struct rcu_data *rdp = this_cpu_ptr(&rcu_data); > > @@ -651,25 +653,15 @@ static __always_inline void rcu_nmi_exit_common(bool irq) > trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, atomic_read(&rdp->dynticks)); > WRITE_ONCE(rdp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */ > > - if (irq) > + if (!in_nmi()) > rcu_prepare_for_idle(); > > rcu_dynticks_eqs_enter(); > > - if (irq) > + if (!in_nmi()) > rcu_dynticks_task_enter(); > } Boris and me have been going over the #MC code (and finding loads of 'interesting' code) and ran into ist_enter(), whish has the following code: /* * We might have interrupted pretty much anything. In * fact, if we're a machine check, we can even interrupt * NMI processing. We don't want in_nmi() to return true, * but we need to notify RCU. */ rcu_nmi_enter(); Which, to me, sounds all sorts of broken. The IST (be it #DB or #MC) can happen while we're holding all sorts of locks. This must be an NMI-like context. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bombadil.infradead.org ([198.137.202.133]:33422 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728337AbgBRT65 (ORCPT ); Tue, 18 Feb 2020 14:58:57 -0500 Date: Tue, 18 Feb 2020 20:58:31 +0100 From: Peter Zijlstra Subject: Re: [PATCH v2 3/9] rcu,tracing: Create trace_rcu_{enter,exit}() Message-ID: <20200218195831.GD11457@worktop.programming.kicks-ass.net> References: <20200212210139.382424693@infradead.org> <20200212210749.971717428@infradead.org> <20200212232005.GC115917@google.com> <20200213082716.GI14897@hirez.programming.kicks-ass.net> <20200213135138.GB2935@paulmck-ThinkPad-P72> <20200213164031.GH14914@hirez.programming.kicks-ass.net> <20200213185612.GG2935@paulmck-ThinkPad-P72> <20200213204444.GA94647@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200213204444.GA94647@google.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Joel Fernandes Cc: "Paul E. McKenney" , linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, rostedt@goodmis.org, mingo@kernel.org, gregkh@linuxfoundation.org, gustavo@embeddedor.com, tglx@linutronix.de, josh@joshtriplett.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com Message-ID: <20200218195831.uv31Q-L70Zx6xlCzMZxXD92f2Saus2RKuIkx0mzNls0@z> On Thu, Feb 13, 2020 at 03:44:44PM -0500, Joel Fernandes wrote: > > > That _should_ already be the case today. That is, if we end up in a > > > tracer and in_nmi() is unreliable we're already screwed anyway. > I removed the static from rcu_nmi_enter()/exit() as it is called from > outside, that makes it build now. Updated below is Paul's diff. I also added > NOKPROBE_SYMBOL() to rcu_nmi_exit() to match rcu_nmi_enter() since it seemed > asymmetric. > +__always_inline void rcu_nmi_exit(void) > { > struct rcu_data *rdp = this_cpu_ptr(&rcu_data); > > @@ -651,25 +653,15 @@ static __always_inline void rcu_nmi_exit_common(bool irq) > trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, atomic_read(&rdp->dynticks)); > WRITE_ONCE(rdp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */ > > - if (irq) > + if (!in_nmi()) > rcu_prepare_for_idle(); > > rcu_dynticks_eqs_enter(); > > - if (irq) > + if (!in_nmi()) > rcu_dynticks_task_enter(); > } Boris and me have been going over the #MC code (and finding loads of 'interesting' code) and ran into ist_enter(), whish has the following code: /* * We might have interrupted pretty much anything. In * fact, if we're a machine check, we can even interrupt * NMI processing. We don't want in_nmi() to return true, * but we need to notify RCU. */ rcu_nmi_enter(); Which, to me, sounds all sorts of broken. The IST (be it #DB or #MC) can happen while we're holding all sorts of locks. This must be an NMI-like context.