From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id DEE0FC43215 for ; Fri, 15 Nov 2019 22:25:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A1B942073A for ; Fri, 15 Nov 2019 22:25:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573856706; bh=HVIIr56nYSAJIBDSratfjG4I/R8T/8LpSDDbBjkuMnE=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:List-ID: From; b=m8aQiaLlxmWCOhRj5VfTWvkRUHTIdquIoA4Y20AQBuUKAXjmPd/HvMHMlSCrCPU+w 73q4BrwG6dJLfy0lKsstKrgE2AtezZrwTVRDA+iTTQlacN7hD9pT9Oc8gMszmbNJw5 3zQC6BUIh240wtyNobAxUPjzZi/g/lpJoC84gssY= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727056AbfKOWZF (ORCPT ); Fri, 15 Nov 2019 17:25:05 -0500 Received: from mail.kernel.org ([198.145.29.99]:56090 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726766AbfKOWZF (ORCPT ); Fri, 15 Nov 2019 17:25:05 -0500 Received: from paulmck-ThinkPad-P72.home (unknown [199.201.64.129]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8EB1920733; Fri, 15 Nov 2019 22:25:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1573856704; bh=HVIIr56nYSAJIBDSratfjG4I/R8T/8LpSDDbBjkuMnE=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=IagDsTcNy8KaWnqM5nMptvN1QrMfN1/71lWYvfqzN6Wyj4zwZ51psjkP6fmXlsmZP tAJAbbFy3Lamm6oUVrTTHHmvj/RkrQprGlbg3gxcEkdz2YSnpiM60+X/ABoig23lKF +UHydMHtlYrCeszDIAwYmG83UqhHFy/7qZiq2+1s= Received: by paulmck-ThinkPad-P72.home (Postfix, from userid 1000) id DAF0E35227A8; Fri, 15 Nov 2019 14:25:03 -0800 (PST) Date: Fri, 15 Nov 2019 14:25:03 -0800 From: "Paul E. McKenney" To: Lai Jiangshan Cc: linux-kernel@vger.kernel.org, Josh Triplett , Steven Rostedt , Mathieu Desnoyers , Lai Jiangshan , Joel Fernandes , rcu@vger.kernel.org Subject: Re: [PATCH V2 5/7] rcu: wrap usages of rcu_read_lock_nesting Message-ID: <20191115222503.GA2865@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20191102124559.1135-1-laijs@linux.alibaba.com> <20191102124559.1135-6-laijs@linux.alibaba.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191102124559.1135-6-laijs@linux.alibaba.com> User-Agent: Mutt/1.9.4 (2018-02-28) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Nov 02, 2019 at 12:45:57PM +0000, Lai Jiangshan wrote: > Prepare for using percpu rcu_preempt_depth on x86 This one makes a lot of sense just by itself -- I probably should have done something like this years ago. I hand-applied this due to conflicts from not having the earlier commits. Please see comments inline. The resulting patch is at the end, so please let me know if I messed anything up. > Signed-off-by: Lai Jiangshan > --- > kernel/rcu/tree_exp.h | 4 ++-- > kernel/rcu/tree_plugin.h | 43 ++++++++++++++++++++++++++-------------- > 2 files changed, 30 insertions(+), 17 deletions(-) > > diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h > index afa9f573b00f..dcb2124203cf 100644 > --- a/kernel/rcu/tree_exp.h > +++ b/kernel/rcu/tree_exp.h > @@ -608,7 +608,7 @@ static void rcu_exp_handler(void *unused) > * critical section. If also enabled or idle, immediately > * report the quiescent state, otherwise defer. > */ > - if (!t->rcu_read_lock_nesting) { > + if (!rcu_preempt_depth()) { > rdp->exp_deferred_qs = true; > if (!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)) || > rcu_dynticks_curr_cpu_in_eqs()) { > @@ -632,7 +632,7 @@ static void rcu_exp_handler(void *unused) > * can have caused this quiescent state to already have been > * reported, so we really do need to check ->expmask. > */ > - if (t->rcu_read_lock_nesting > 0) { > + if (rcu_preempt_depth() > 0) { > raw_spin_lock_irqsave_rcu_node(rnp, flags); > if (rnp->expmask & rdp->grpmask) { > rdp->exp_deferred_qs = true; > diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h > index 98644966c808..eb5906c55c8d 100644 > --- a/kernel/rcu/tree_plugin.h > +++ b/kernel/rcu/tree_plugin.h > @@ -290,8 +290,8 @@ void rcu_note_context_switch(bool preempt) > > trace_rcu_utilization(TPS("Start context switch")); > lockdep_assert_irqs_disabled(); > - WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0); > - if (t->rcu_read_lock_nesting > 0 && > + WARN_ON_ONCE(!preempt && rcu_preempt_depth() > 0); > + if (rcu_preempt_depth() > 0 && > !t->rcu_read_unlock_special.b.blocked) { > > /* Possibly blocking in an RCU read-side critical section. */ > @@ -346,6 +346,21 @@ static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) > /* Bias and limit values for ->rcu_read_lock_nesting. */ > #define RCU_NEST_PMAX (INT_MAX / 2) > > +static inline void rcu_preempt_depth_inc(void) > +{ > + current->rcu_read_lock_nesting++; > +} > + > +static inline bool rcu_preempt_depth_dec_and_test(void) > +{ > + return --current->rcu_read_lock_nesting == 0; > +} I made an rcu_preempt_depth_dec() for the time being. Hopefully we can get something set up to require rcu_preempt_depth_dec_and_test() soon, but we are not there yet. > +static inline void rcu_preempt_depth_set(int val) > +{ > + current->rcu_read_lock_nesting = val; > +} These can just be static (rather than static inline) because this .h file is included into only one .c file. Best to let the compiler make the inlining decisions. > /* > * Preemptible RCU implementation for rcu_read_lock(). > * Just increment ->rcu_read_lock_nesting, shared state will be updated > @@ -353,9 +368,9 @@ static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) > */ > void __rcu_read_lock(void) > { > - current->rcu_read_lock_nesting++; > + rcu_preempt_depth_inc(); > if (IS_ENABLED(CONFIG_PROVE_LOCKING)) > - WARN_ON_ONCE(current->rcu_read_lock_nesting > RCU_NEST_PMAX); > + WARN_ON_ONCE(rcu_preempt_depth() > RCU_NEST_PMAX); > barrier(); /* critical section after entry code. */ > } > EXPORT_SYMBOL_GPL(__rcu_read_lock); > @@ -371,15 +386,13 @@ void __rcu_read_unlock(void) > { > struct task_struct *t = current; > > - if (--t->rcu_read_lock_nesting == 0) { > + if (rcu_preempt_depth_dec_and_test()) { > barrier(); /* critical section before exit code. */ > if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s))) > rcu_read_unlock_special(t); > } > if (IS_ENABLED(CONFIG_PROVE_LOCKING)) { > - int rrln = t->rcu_read_lock_nesting; > - > - WARN_ON_ONCE(rrln < 0); > + WARN_ON_ONCE(rcu_preempt_depth() < 0); > } > } > EXPORT_SYMBOL_GPL(__rcu_read_unlock); > @@ -531,7 +544,7 @@ static bool rcu_preempt_need_deferred_qs(struct task_struct *t) > { > return (__this_cpu_read(rcu_data.exp_deferred_qs) || > READ_ONCE(t->rcu_read_unlock_special.s)) && > - !t->rcu_read_lock_nesting; > + !rcu_preempt_depth(); > } > > /* > @@ -662,7 +675,7 @@ static void rcu_flavor_sched_clock_irq(int user) > if (user || rcu_is_cpu_rrupt_from_idle()) { > rcu_note_voluntary_context_switch(current); > } > - if (t->rcu_read_lock_nesting > 0 || > + if (rcu_preempt_depth() > 0 || > (preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK))) { > /* No QS, force context switch if deferred. */ > if (rcu_preempt_need_deferred_qs(t)) { > @@ -672,13 +685,13 @@ static void rcu_flavor_sched_clock_irq(int user) > } else if (rcu_preempt_need_deferred_qs(t)) { > rcu_preempt_deferred_qs(t); /* Report deferred QS. */ > return; > - } else if (!t->rcu_read_lock_nesting) { > + } else if (!rcu_preempt_depth()) { > rcu_qs(); /* Report immediate QS. */ > return; > } > > /* If GP is oldish, ask for help from rcu_read_unlock_special(). */ > - if (t->rcu_read_lock_nesting > 0 && > + if (rcu_preempt_depth() > 0 && > __this_cpu_read(rcu_data.core_needs_qs) && > __this_cpu_read(rcu_data.cpu_no_qs.b.norm) && > !t->rcu_read_unlock_special.b.need_qs && > @@ -699,11 +712,11 @@ void exit_rcu(void) > struct task_struct *t = current; > > if (unlikely(!list_empty(¤t->rcu_node_entry))) { > - t->rcu_read_lock_nesting = 1; > + rcu_preempt_depth_set(1); > barrier(); > WRITE_ONCE(t->rcu_read_unlock_special.b.blocked, true); > - } else if (unlikely(t->rcu_read_lock_nesting)) { > - t->rcu_read_lock_nesting = 1; > + } else if (unlikely(rcu_preempt_depth())) { > + rcu_preempt_depth_set(1); > } else { > return; > } > -- > 2.20.1 ------------------------------------------------------------------------ commit 2f19afd3450c855007e1b355df6f215a0477d809 Author: Lai Jiangshan Date: Fri Nov 15 14:08:53 2019 -0800 rcu: Provide wrappers for uses of ->rcu_read_lock_nesting This commit provides wrapper functions for uses of ->rcu_read_lock_nesting to improve readability and to ease future changes to support inlining of __rcu_read_lock() and __rcu_read_unlock(). Signed-off-by: Lai Jiangshan Signed-off-by: Paul E. McKenney diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index e4b77d3..6ce598d 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -608,7 +608,7 @@ static void rcu_exp_handler(void *unused) * critical section. If also enabled or idle, immediately * report the quiescent state, otherwise defer. */ - if (!t->rcu_read_lock_nesting) { + if (!rcu_preempt_depth()) { if (!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)) || rcu_dynticks_curr_cpu_in_eqs()) { rcu_report_exp_rdp(rdp); @@ -632,7 +632,7 @@ static void rcu_exp_handler(void *unused) * can have caused this quiescent state to already have been * reported, so we really do need to check ->expmask. */ - if (t->rcu_read_lock_nesting > 0) { + if (rcu_preempt_depth() > 0) { raw_spin_lock_irqsave_rcu_node(rnp, flags); if (rnp->expmask & rdp->grpmask) { rdp->exp_deferred_qs = true; diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 96dc3aa..b5605bd 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -292,8 +292,8 @@ void rcu_note_context_switch(bool preempt) trace_rcu_utilization(TPS("Start context switch")); lockdep_assert_irqs_disabled(); - WARN_ON_ONCE(!preempt && t->rcu_read_lock_nesting > 0); - if (t->rcu_read_lock_nesting > 0 && + WARN_ON_ONCE(!preempt && rcu_preempt_depth() > 0); + if (rcu_preempt_depth() > 0 && !t->rcu_read_unlock_special.b.blocked) { /* Possibly blocking in an RCU read-side critical section. */ @@ -350,6 +350,21 @@ static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) #define RCU_NEST_NMAX (-INT_MAX / 2) #define RCU_NEST_PMAX (INT_MAX / 2) +static void rcu_preempt_read_enter(void) +{ + current->rcu_read_lock_nesting++; +} + +static void rcu_preempt_read_exit(void) +{ + current->rcu_read_lock_nesting--; +} + +static void rcu_preempt_depth_set(int val) +{ + current->rcu_read_lock_nesting = val; +} + /* * Preemptible RCU implementation for rcu_read_lock(). * Just increment ->rcu_read_lock_nesting, shared state will be updated @@ -357,9 +372,9 @@ static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp) */ void __rcu_read_lock(void) { - current->rcu_read_lock_nesting++; + rcu_preempt_read_enter(); if (IS_ENABLED(CONFIG_PROVE_LOCKING)) - WARN_ON_ONCE(current->rcu_read_lock_nesting > RCU_NEST_PMAX); + WARN_ON_ONCE(rcu_preempt_depth() > RCU_NEST_PMAX); barrier(); /* critical section after entry code. */ } EXPORT_SYMBOL_GPL(__rcu_read_lock); @@ -375,19 +390,19 @@ void __rcu_read_unlock(void) { struct task_struct *t = current; - if (t->rcu_read_lock_nesting != 1) { - --t->rcu_read_lock_nesting; + if (rcu_preempt_depth() != 1) { + rcu_preempt_read_exit(); } else { barrier(); /* critical section before exit code. */ - t->rcu_read_lock_nesting = -RCU_NEST_BIAS; + rcu_preempt_depth_set(-RCU_NEST_BIAS); barrier(); /* assign before ->rcu_read_unlock_special load */ if (unlikely(READ_ONCE(t->rcu_read_unlock_special.s))) rcu_read_unlock_special(t); barrier(); /* ->rcu_read_unlock_special load before assign */ - t->rcu_read_lock_nesting = 0; + rcu_preempt_depth_set(0); } if (IS_ENABLED(CONFIG_PROVE_LOCKING)) { - int rrln = t->rcu_read_lock_nesting; + int rrln = rcu_preempt_depth(); WARN_ON_ONCE(rrln < 0 && rrln > RCU_NEST_NMAX); } @@ -541,7 +556,7 @@ static bool rcu_preempt_need_deferred_qs(struct task_struct *t) { return (__this_cpu_read(rcu_data.exp_deferred_qs) || READ_ONCE(t->rcu_read_unlock_special.s)) && - t->rcu_read_lock_nesting <= 0; + rcu_preempt_depth() <= 0; } /* @@ -554,16 +569,16 @@ static bool rcu_preempt_need_deferred_qs(struct task_struct *t) static void rcu_preempt_deferred_qs(struct task_struct *t) { unsigned long flags; - bool couldrecurse = t->rcu_read_lock_nesting >= 0; + bool couldrecurse = rcu_preempt_depth() >= 0; if (!rcu_preempt_need_deferred_qs(t)) return; if (couldrecurse) - t->rcu_read_lock_nesting -= RCU_NEST_BIAS; + rcu_preempt_depth_set(rcu_preempt_depth() - RCU_NEST_BIAS); local_irq_save(flags); rcu_preempt_deferred_qs_irqrestore(t, flags); if (couldrecurse) - t->rcu_read_lock_nesting += RCU_NEST_BIAS; + rcu_preempt_depth_set(rcu_preempt_depth() + RCU_NEST_BIAS); } /* @@ -674,7 +689,7 @@ static void rcu_flavor_sched_clock_irq(int user) if (user || rcu_is_cpu_rrupt_from_idle()) { rcu_note_voluntary_context_switch(current); } - if (t->rcu_read_lock_nesting > 0 || + if (rcu_preempt_depth() > 0 || (preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK))) { /* No QS, force context switch if deferred. */ if (rcu_preempt_need_deferred_qs(t)) { @@ -684,13 +699,13 @@ static void rcu_flavor_sched_clock_irq(int user) } else if (rcu_preempt_need_deferred_qs(t)) { rcu_preempt_deferred_qs(t); /* Report deferred QS. */ return; - } else if (!t->rcu_read_lock_nesting) { + } else if (!rcu_preempt_depth()) { rcu_qs(); /* Report immediate QS. */ return; } /* If GP is oldish, ask for help from rcu_read_unlock_special(). */ - if (t->rcu_read_lock_nesting > 0 && + if (rcu_preempt_depth() > 0 && __this_cpu_read(rcu_data.core_needs_qs) && __this_cpu_read(rcu_data.cpu_no_qs.b.norm) && !t->rcu_read_unlock_special.b.need_qs && @@ -711,11 +726,11 @@ void exit_rcu(void) struct task_struct *t = current; if (unlikely(!list_empty(¤t->rcu_node_entry))) { - t->rcu_read_lock_nesting = 1; + rcu_preempt_depth_set(1); barrier(); WRITE_ONCE(t->rcu_read_unlock_special.b.blocked, true); - } else if (unlikely(t->rcu_read_lock_nesting)) { - t->rcu_read_lock_nesting = 1; + } else if (unlikely(rcu_preempt_depth())) { + rcu_preempt_depth_set(1); } else { return; }