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=-10.1 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_GIT 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 675D1C2BA19 for ; Wed, 15 Apr 2020 18:22:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 40F4C2076D for ; Wed, 15 Apr 2020 18:22:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586974967; bh=Mg9UGLEn+8mKQiBDb5bnhsQsD+0riRG6qzZI4sDA8xk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=WnoxVF1vxKd0vqy7KtdcLExKJIsjV5rcNbmbB3BCZ964m7D7Pg356GjTMMwucdrdq Nfuq5fD7WsO32Otb3GJEc4yIYjuw6suFkT6XZoOIJ8IDG1V6+Fvd/jW6IfhGt8LVVS 9wCgftUWP7P62AfrewnMGPALv+ayiV0s6/nDy8jA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1416634AbgDOSWp (ORCPT ); Wed, 15 Apr 2020 14:22:45 -0400 Received: from mail.kernel.org ([198.145.29.99]:37248 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2441386AbgDOSTx (ORCPT ); Wed, 15 Apr 2020 14:19:53 -0400 Received: from paulmck-ThinkPad-P72.home (50-39-105-78.bvtn.or.frontiernet.net [50.39.105.78]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id C33C121973; Wed, 15 Apr 2020 18:19:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1586974792; bh=Mg9UGLEn+8mKQiBDb5bnhsQsD+0riRG6qzZI4sDA8xk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=SRwut/nqBwGTFjwQ0mBHEbVMmLC4o6vo0mN7nk2X4qtSZI8xBZXWUnmqYy7pzUKsU X5tJx7sYg65nVUjL9ItufWTwaFB55CZ4oBGDz3vgcInqH0py8OzqGN5FKhBp7N+7fu ShrLDqPdCcXTjvficjZhdnw1zwQK/W+s2dquxq0s= From: paulmck@kernel.org To: rcu@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com, akpm@linux-foundation.org, mathieu.desnoyers@efficios.com, josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org, rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org, "Paul E. McKenney" Subject: [PATCH v4 tip/core/rcu 24/38] rcu-tasks: Split ->trc_reader_need_end Date: Wed, 15 Apr 2020 11:19:27 -0700 Message-Id: <20200415181941.11653-24-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20200415181856.GA11037@paulmck-ThinkPad-P72> References: <20200415181856.GA11037@paulmck-ThinkPad-P72> Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Paul E. McKenney" This commit splits ->trc_reader_need_end by using the rcu_special union. This change permits readers to check to see if a memory barrier is required without any added overhead in the common case where no such barrier is required. This commit also adds the read-side checking. Later commits will add the machinery to properly set the new ->trc_reader_special.b.need_mb field. This commit also makes rcu_read_unlock_trace_special() tolerate nested read-side critical sections within interrupt and NMI handlers. Signed-off-by: Paul E. McKenney --- include/linux/rcupdate_trace.h | 11 +++++++---- include/linux/sched.h | 4 ++-- init/init_task.c | 1 + kernel/fork.c | 1 + kernel/rcu/tasks.h | 33 ++++++++++++++++++++------------- 5 files changed, 31 insertions(+), 19 deletions(-) diff --git a/include/linux/rcupdate_trace.h b/include/linux/rcupdate_trace.h index ed97e10..c42b365c 100644 --- a/include/linux/rcupdate_trace.h +++ b/include/linux/rcupdate_trace.h @@ -31,7 +31,7 @@ static inline int rcu_read_lock_trace_held(void) #ifdef CONFIG_TASKS_TRACE_RCU -void rcu_read_unlock_trace_special(struct task_struct *t); +void rcu_read_unlock_trace_special(struct task_struct *t, int nesting); /** * rcu_read_lock_trace - mark beginning of RCU-trace read-side critical section @@ -50,6 +50,8 @@ static inline void rcu_read_lock_trace(void) struct task_struct *t = current; WRITE_ONCE(t->trc_reader_nesting, READ_ONCE(t->trc_reader_nesting) + 1); + if (t->trc_reader_special.b.need_mb) + smp_mb(); // Pairs with update-side barriers rcu_lock_acquire(&rcu_trace_lock_map); } @@ -69,10 +71,11 @@ static inline void rcu_read_unlock_trace(void) rcu_lock_release(&rcu_trace_lock_map); nesting = READ_ONCE(t->trc_reader_nesting) - 1; - WRITE_ONCE(t->trc_reader_nesting, nesting); - if (likely(!READ_ONCE(t->trc_reader_need_end)) || nesting) + if (likely(!READ_ONCE(t->trc_reader_special.s)) || nesting) { + WRITE_ONCE(t->trc_reader_nesting, nesting); return; // We assume shallow reader nesting. - rcu_read_unlock_trace_special(t); + } + rcu_read_unlock_trace_special(t, nesting); } void call_rcu_tasks_trace(struct rcu_head *rhp, rcu_callback_t func); diff --git a/include/linux/sched.h b/include/linux/sched.h index 864f60e..9437b53 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -613,7 +613,7 @@ union rcu_special { u8 blocked; u8 need_qs; u8 exp_hint; /* Hint for performance. */ - u8 pad; /* No garbage from compiler! */ + u8 need_mb; /* Readers need smp_mb(). */ } b; /* Bits. */ u32 s; /* Set of bits. */ }; @@ -727,7 +727,7 @@ struct task_struct { #ifdef CONFIG_TASKS_TRACE_RCU int trc_reader_nesting; int trc_ipi_to_cpu; - bool trc_reader_need_end; + union rcu_special trc_reader_special; bool trc_reader_checked; struct list_head trc_holdout_list; #endif /* #ifdef CONFIG_TASKS_TRACE_RCU */ diff --git a/init/init_task.c b/init/init_task.c index e8b3740..825972d 100644 --- a/init/init_task.c +++ b/init/init_task.c @@ -143,6 +143,7 @@ struct task_struct init_task #endif #ifdef CONFIG_TASKS_TRACE_RCU .trc_reader_nesting = 0, + .trc_reader_special.s = 0, .trc_holdout_list = LIST_HEAD_INIT(init_task.trc_holdout_list), #endif #ifdef CONFIG_CPUSETS diff --git a/kernel/fork.c b/kernel/fork.c index 1eff609..559cdb1 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -1685,6 +1685,7 @@ static inline void rcu_copy_process(struct task_struct *p) #endif /* #ifdef CONFIG_TASKS_RCU */ #ifdef CONFIG_TASKS_TRACE_RCU p->trc_reader_nesting = 0; + p->trc_reader_special.s = 0; INIT_LIST_HEAD(&p->trc_holdout_list); #endif /* #ifdef CONFIG_TASKS_TRACE_RCU */ } diff --git a/kernel/rcu/tasks.h b/kernel/rcu/tasks.h index 6f4e8b1..4a730f1 100644 --- a/kernel/rcu/tasks.h +++ b/kernel/rcu/tasks.h @@ -723,10 +723,17 @@ DEFINE_RCU_TASKS(rcu_tasks_trace, rcu_tasks_wait_gp, call_rcu_tasks_trace, "RCU Tasks Trace"); /* If we are the last reader, wake up the grace-period kthread. */ -void rcu_read_unlock_trace_special(struct task_struct *t) +void rcu_read_unlock_trace_special(struct task_struct *t, int nesting) { - WRITE_ONCE(t->trc_reader_need_end, false); - if (atomic_dec_and_test(&trc_n_readers_need_end)) + int nq = t->trc_reader_special.b.need_qs; + + if (t->trc_reader_special.b.need_mb) + smp_mb(); // Pairs with update-side barriers. + // Update .need_qs before ->trc_reader_nesting for irq/NMI handlers. + if (nq) + WRITE_ONCE(t->trc_reader_special.b.need_qs, false); + WRITE_ONCE(t->trc_reader_nesting, nesting); + if (nq && atomic_dec_and_test(&trc_n_readers_need_end)) wake_up(&trc_wait); } EXPORT_SYMBOL_GPL(rcu_read_unlock_trace_special); @@ -777,8 +784,8 @@ static void trc_read_check_handler(void *t_in) // Get here if the task is in a read-side critical section. Set // its state so that it will awaken the grace-period kthread upon // exit from that critical section. - WARN_ON_ONCE(t->trc_reader_need_end); - WRITE_ONCE(t->trc_reader_need_end, true); + WARN_ON_ONCE(t->trc_reader_special.b.need_qs); + WRITE_ONCE(t->trc_reader_special.b.need_qs, true); reset_ipi: // Allow future IPIs to be sent on CPU and for task. @@ -804,8 +811,8 @@ static bool trc_inspect_reader(struct task_struct *t, void *arg) // exit from that critical section. if (unlikely(t->trc_reader_nesting)) { atomic_inc(&trc_n_readers_need_end); // One more to wait on. - WARN_ON_ONCE(t->trc_reader_need_end); - WRITE_ONCE(t->trc_reader_need_end, true); + WARN_ON_ONCE(t->trc_reader_special.b.need_qs); + WRITE_ONCE(t->trc_reader_special.b.need_qs, true); } return true; } @@ -880,7 +887,7 @@ static void rcu_tasks_trace_pregp_step(void) static void rcu_tasks_trace_pertask(struct task_struct *t, struct list_head *hop) { - WRITE_ONCE(t->trc_reader_need_end, false); + WRITE_ONCE(t->trc_reader_special.b.need_qs, false); WRITE_ONCE(t->trc_reader_checked, false); t->trc_ipi_to_cpu = -1; trc_wait_for_one_reader(t, hop); @@ -912,7 +919,7 @@ static void show_stalled_task_trace(struct task_struct *t, bool *firstreport) ".i"[is_idle_task(t)], ".N"[cpu > 0 && tick_nohz_full_cpu(cpu)], t->trc_reader_nesting, - " N"[!!t->trc_reader_need_end], + " N"[!!t->trc_reader_special.b.need_qs], cpu); sched_show_task(t); } @@ -976,11 +983,11 @@ static void rcu_tasks_trace_postgp(struct rcu_tasks *rtp) break; // Count reached zero. // Stall warning time, so make a list of the offenders. for_each_process_thread(g, t) - if (READ_ONCE(t->trc_reader_need_end)) + if (READ_ONCE(t->trc_reader_special.b.need_qs)) trc_add_holdout(t, &holdouts); firstreport = true; list_for_each_entry_safe(t, g, &holdouts, trc_holdout_list) - if (READ_ONCE(t->trc_reader_need_end)) { + if (READ_ONCE(t->trc_reader_special.b.need_qs)) { show_stalled_task_trace(t, &firstreport); trc_del_holdout(t); } @@ -999,8 +1006,8 @@ void exit_tasks_rcu_finish_trace(struct task_struct *t) WRITE_ONCE(t->trc_reader_checked, true); WARN_ON_ONCE(t->trc_reader_nesting); WRITE_ONCE(t->trc_reader_nesting, 0); - if (WARN_ON_ONCE(READ_ONCE(t->trc_reader_need_end))) - rcu_read_unlock_trace_special(t); + if (WARN_ON_ONCE(READ_ONCE(t->trc_reader_special.b.need_qs))) + rcu_read_unlock_trace_special(t, 0); } /** -- 2.9.5