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=ham 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 A1742C35242 for ; Fri, 14 Feb 2020 23:56:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7385924649 for ; Fri, 14 Feb 2020 23:56:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581724616; bh=RU3ndbHIcx84N7Zau8RC9Qo/Qt8DFa2SxmpMLPxwJyg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=IF34y9VPk530zwWzZKQPw6uXt3LKkMZcmaUQNtyED00NSLs9XfmxiLrOLFoBo/rcP iULl84vMbwT+9Ki0nxp63aVUAdaEriltluI1mnvZroTLToZPo1f0xD44HFQg1y19Ei B4t7V0tyddD1w1iIXnIkDV78kbqIU7r0aluqpAQw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728080AbgBNX44 (ORCPT ); Fri, 14 Feb 2020 18:56:56 -0500 Received: from mail.kernel.org ([198.145.29.99]:36706 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726164AbgBNX4z (ORCPT ); Fri, 14 Feb 2020 18:56:55 -0500 Received: from paulmck-ThinkPad-P72.c.hoisthospitality.com (unknown [62.84.152.189]) (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 3A41B2081E; Fri, 14 Feb 2020 23:56:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581724614; bh=RU3ndbHIcx84N7Zau8RC9Qo/Qt8DFa2SxmpMLPxwJyg=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Hu0Ic/xkF8CqEnVM/onpWK4erOhmW9SC855EvLe10rr3+ugdzSyVeUVEahpLKShgd P6+gvV3NkYvC9ktQa6AjV7mRdfofVTpeZHApsaiRj+TXl6bWmJIO9RqWhj5RDiqMJI pYpgzVTVsxYcMz88lU/VbhXyIzs/O8cB5hVMEmbA= 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 tip/core/rcu 12/30] rcu: *_ONCE() for grace-period progress indicators Date: Fri, 14 Feb 2020 15:55:49 -0800 Message-Id: <20200214235607.13749-12-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20200214235536.GA13364@paulmck-ThinkPad-P72> References: <20200214235536.GA13364@paulmck-ThinkPad-P72> Sender: rcu-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org From: "Paul E. McKenney" The various RCU structures' ->gp_seq, ->gp_seq_needed, ->gp_req_activity, and ->gp_activity fields are read locklessly, so they must be updated with WRITE_ONCE() and, when read locklessly, with READ_ONCE(). This commit makes these changes. This data race was reported by KCSAN. Not appropriate for backporting due to failure being unlikely. Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 14 +++++++------- kernel/rcu/tree_plugin.h | 2 +- kernel/rcu/tree_stall.h | 26 +++++++++++++++----------- 3 files changed, 23 insertions(+), 19 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 346321a..53946b1 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -1175,7 +1175,7 @@ static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp, TPS("Prestarted")); goto unlock_out; } - rnp->gp_seq_needed = gp_seq_req; + WRITE_ONCE(rnp->gp_seq_needed, gp_seq_req); if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq))) { /* * We just marked the leaf or internal node, and a @@ -1210,8 +1210,8 @@ static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp, unlock_out: /* Push furthest requested GP to leaf node and rcu_data structure. */ if (ULONG_CMP_LT(gp_seq_req, rnp->gp_seq_needed)) { - rnp_start->gp_seq_needed = rnp->gp_seq_needed; - rdp->gp_seq_needed = rnp->gp_seq_needed; + WRITE_ONCE(rnp_start->gp_seq_needed, rnp->gp_seq_needed); + WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed); } if (rnp != rnp_start) raw_spin_unlock_rcu_node(rnp); @@ -1423,7 +1423,7 @@ static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp) } rdp->gp_seq = rnp->gp_seq; /* Remember new grace-period state. */ if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) || rdp->gpwrap) - rdp->gp_seq_needed = rnp->gp_seq_needed; + WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed); WRITE_ONCE(rdp->gpwrap, false); rcu_gpnum_ovf(rnp, rdp); return ret; @@ -3276,12 +3276,12 @@ int rcutree_prepare_cpu(unsigned int cpu) rnp = rdp->mynode; raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */ rdp->beenonline = true; /* We have now been online. */ - rdp->gp_seq = rnp->gp_seq; - rdp->gp_seq_needed = rnp->gp_seq; + rdp->gp_seq = READ_ONCE(rnp->gp_seq); + rdp->gp_seq_needed = rdp->gp_seq; rdp->cpu_no_qs.b.norm = true; rdp->core_needs_qs = false; rdp->rcu_iw_pending = false; - rdp->rcu_iw_gp_seq = rnp->gp_seq - 1; + rdp->rcu_iw_gp_seq = rdp->gp_seq - 1; trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuonl")); raw_spin_unlock_irqrestore_rcu_node(rnp, flags); rcu_prepare_kthreads(cpu); diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index c6ea81c..b5ba148 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -753,7 +753,7 @@ dump_blkd_tasks(struct rcu_node *rnp, int ncheck) raw_lockdep_assert_held_rcu_node(rnp); pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n", __func__, rnp->grplo, rnp->grphi, rnp->level, - (long)rnp->gp_seq, (long)rnp->completedqs); + (long)READ_ONCE(rnp->gp_seq), (long)rnp->completedqs); for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent) pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx\n", __func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext); diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index 55f9b84..3dcbecf 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -592,21 +592,22 @@ void show_rcu_gp_kthreads(void) (long)READ_ONCE(rcu_get_root()->gp_seq_needed), READ_ONCE(rcu_state.gp_flags)); rcu_for_each_node_breadth_first(rnp) { - if (ULONG_CMP_GE(rcu_state.gp_seq, rnp->gp_seq_needed)) + if (ULONG_CMP_GE(READ_ONCE(rcu_state.gp_seq), + READ_ONCE(rnp->gp_seq_needed))) continue; pr_info("\trcu_node %d:%d ->gp_seq %ld ->gp_seq_needed %ld\n", - rnp->grplo, rnp->grphi, (long)rnp->gp_seq, - (long)rnp->gp_seq_needed); + rnp->grplo, rnp->grphi, (long)READ_ONCE(rnp->gp_seq), + (long)READ_ONCE(rnp->gp_seq_needed)); if (!rcu_is_leaf_node(rnp)) continue; for_each_leaf_node_possible_cpu(rnp, cpu) { rdp = per_cpu_ptr(&rcu_data, cpu); if (rdp->gpwrap || - ULONG_CMP_GE(rcu_state.gp_seq, - rdp->gp_seq_needed)) + ULONG_CMP_GE(READ_ONCE(rcu_state.gp_seq), + READ_ONCE(rdp->gp_seq_needed))) continue; pr_info("\tcpu %d ->gp_seq_needed %ld\n", - cpu, (long)rdp->gp_seq_needed); + cpu, (long)READ_ONCE(rdp->gp_seq_needed)); } } for_each_possible_cpu(cpu) { @@ -631,7 +632,8 @@ static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp, static atomic_t warned = ATOMIC_INIT(0); if (!IS_ENABLED(CONFIG_PROVE_RCU) || rcu_gp_in_progress() || - ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed)) + ULONG_CMP_GE(READ_ONCE(rnp_root->gp_seq), + READ_ONCE(rnp_root->gp_seq_needed))) return; j = jiffies; /* Expensive access, and in common case don't get here. */ if (time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) || @@ -642,7 +644,8 @@ static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp, raw_spin_lock_irqsave_rcu_node(rnp, flags); j = jiffies; if (rcu_gp_in_progress() || - ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) || + ULONG_CMP_GE(READ_ONCE(rnp_root->gp_seq), + READ_ONCE(rnp_root->gp_seq_needed)) || time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) || time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) || atomic_read(&warned)) { @@ -655,9 +658,10 @@ static void rcu_check_gp_start_stall(struct rcu_node *rnp, struct rcu_data *rdp, raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */ j = jiffies; if (rcu_gp_in_progress() || - ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) || - time_before(j, rcu_state.gp_req_activity + gpssdelay) || - time_before(j, rcu_state.gp_activity + gpssdelay) || + ULONG_CMP_GE(READ_ONCE(rnp_root->gp_seq), + READ_ONCE(rnp_root->gp_seq_needed)) || + time_before(j, READ_ONCE(rcu_state.gp_req_activity) + gpssdelay) || + time_before(j, READ_ONCE(rcu_state.gp_activity) + gpssdelay) || atomic_xchg(&warned, 1)) { if (rnp_root != rnp) /* irqs remain disabled. */ -- 2.9.5