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=-19.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,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 9F2FEC4332B for ; Thu, 4 Mar 2021 01:09:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7B81164EE8 for ; Thu, 4 Mar 2021 01:09:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1353125AbhCDBC7 (ORCPT ); Wed, 3 Mar 2021 20:02:59 -0500 Received: from mail.kernel.org ([198.145.29.99]:45552 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1355385AbhCDAXx (ORCPT ); Wed, 3 Mar 2021 19:23:53 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id E3B7064E56; Thu, 4 Mar 2021 00:23:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1614817393; bh=8WQ3g84kz0p7iNJ8Gkk4N31oVvyO11luf0iCST2rRRA=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=nO41dFOs9w27yceah41akY/YYnxPN2+ty6iVhuiTaYLWjDPsWKafUXUlov2GXRqmJ abvZe7m7ZjSzfjEsKgw1kcj1CipurUwWgA6lsIcbgGqlCutDo5lbtxJghSPcdsTHer O2hX4QEuxcu2nn/w+AAzlfTxngvwx7jkvPTS/mod2nBCibbe5pN6cCoclHsonYinae S4p/eeex9AxDICYW7SNfmM6CbHm4Ha8WmJ0taPsRH7BQ3mLB4XKcDYH3FEMphjCZ+l i307rxr/Q80qyjF8eALgGGJIj/MfuWBd14E0RwzWs60bRcYxOSiMLk+vfnCsUOxURt VDz691mLPRFgQ== 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, 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, Frederic Weisbecker , Neeraj Upadhyay , Boqun Feng , "Paul E . McKenney" Subject: [PATCH tip/core/rcu 01/12] rcu/nocb: Detect unsafe checks for offloaded rdp Date: Wed, 3 Mar 2021 16:23:00 -0800 Message-Id: <20210304002311.23655-1-paulmck@kernel.org> X-Mailer: git-send-email 2.9.5 In-Reply-To: <20210304002225.GA23492@paulmck-ThinkPad-P72> References: <20210304002225.GA23492@paulmck-ThinkPad-P72> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Frederic Weisbecker Provide CONFIG_PROVE_RCU sanity checks to ensure we are always reading the offloaded state of an rdp in a safe and stable way and prevent from its value to be changed under us. We must either hold the barrier mutex, the cpu-hotplug lock (read or write) or the nocb lock. Local non-preemptible reads are also safe. NOCB kthreads and timers have their own means of synchronization against the offloaded state updaters. Cc: Josh Triplett Cc: Steven Rostedt Cc: Mathieu Desnoyers Cc: Lai Jiangshan Cc: Joel Fernandes Cc: Neeraj Upadhyay Cc: Thomas Gleixner Cc: Boqun Feng Signed-off-by: Frederic Weisbecker Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.c | 21 +++++------ kernel/rcu/tree_plugin.h | 90 ++++++++++++++++++++++++++++++++++++++++-------- 2 files changed, 87 insertions(+), 24 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index da6f521..03503e2 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -156,6 +156,7 @@ static void invoke_rcu_core(void); static void rcu_report_exp_rdp(struct rcu_data *rdp); static void sync_sched_exp_online_cleanup(int cpu); static void check_cb_ovld_locked(struct rcu_data *rdp, struct rcu_node *rnp); +static bool rcu_rdp_is_offloaded(struct rcu_data *rdp); /* rcuc/rcub kthread realtime priority */ static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0; @@ -1672,7 +1673,7 @@ static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp) { bool ret = false; bool need_qs; - const bool offloaded = rcu_segcblist_is_offloaded(&rdp->cblist); + const bool offloaded = rcu_rdp_is_offloaded(rdp); raw_lockdep_assert_held_rcu_node(rnp); @@ -2128,7 +2129,7 @@ static void rcu_gp_cleanup(void) needgp = true; } /* Advance CBs to reduce false positives below. */ - offloaded = rcu_segcblist_is_offloaded(&rdp->cblist); + offloaded = rcu_rdp_is_offloaded(rdp); if ((offloaded || !rcu_accelerate_cbs(rnp, rdp)) && needgp) { WRITE_ONCE(rcu_state.gp_flags, RCU_GP_FLAG_INIT); WRITE_ONCE(rcu_state.gp_req_activity, jiffies); @@ -2327,7 +2328,7 @@ rcu_report_qs_rdp(struct rcu_data *rdp) unsigned long flags; unsigned long mask; bool needwake = false; - const bool offloaded = rcu_segcblist_is_offloaded(&rdp->cblist); + const bool offloaded = rcu_rdp_is_offloaded(rdp); struct rcu_node *rnp; WARN_ON_ONCE(rdp->cpu != smp_processor_id()); @@ -2497,7 +2498,7 @@ static void rcu_do_batch(struct rcu_data *rdp) int div; bool __maybe_unused empty; unsigned long flags; - const bool offloaded = rcu_segcblist_is_offloaded(&rdp->cblist); + const bool offloaded = rcu_rdp_is_offloaded(rdp); struct rcu_head *rhp; struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl); long bl, count = 0; @@ -3066,7 +3067,7 @@ __call_rcu(struct rcu_head *head, rcu_callback_t func) trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCBQueued")); /* Go handle any RCU core processing required. */ - if (unlikely(rcu_segcblist_is_offloaded(&rdp->cblist))) { + if (unlikely(rcu_rdp_is_offloaded(rdp))) { __call_rcu_nocb_wake(rdp, was_alldone, flags); /* unlocks */ } else { __call_rcu_core(rdp, head, flags); @@ -3843,13 +3844,13 @@ static int rcu_pending(int user) return 1; /* Does this CPU have callbacks ready to invoke? */ - if (!rcu_segcblist_is_offloaded(&rdp->cblist) && + if (!rcu_rdp_is_offloaded(rdp) && rcu_segcblist_ready_cbs(&rdp->cblist)) return 1; /* Has RCU gone idle with this CPU needing another grace period? */ if (!gp_in_progress && rcu_segcblist_is_enabled(&rdp->cblist) && - !rcu_segcblist_is_offloaded(&rdp->cblist) && + !rcu_rdp_is_offloaded(rdp) && !rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL)) return 1; @@ -3968,7 +3969,7 @@ void rcu_barrier(void) for_each_possible_cpu(cpu) { rdp = per_cpu_ptr(&rcu_data, cpu); if (cpu_is_offline(cpu) && - !rcu_segcblist_is_offloaded(&rdp->cblist)) + !rcu_rdp_is_offloaded(rdp)) continue; if (rcu_segcblist_n_cbs(&rdp->cblist) && cpu_online(cpu)) { rcu_barrier_trace(TPS("OnlineQ"), cpu, @@ -4291,7 +4292,7 @@ void rcutree_migrate_callbacks(int cpu) struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); bool needwake; - if (rcu_segcblist_is_offloaded(&rdp->cblist) || + if (rcu_rdp_is_offloaded(rdp) || rcu_segcblist_empty(&rdp->cblist)) return; /* No callbacks to migrate. */ @@ -4309,7 +4310,7 @@ void rcutree_migrate_callbacks(int cpu) rcu_segcblist_disable(&rdp->cblist); WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) != !rcu_segcblist_n_cbs(&my_rdp->cblist)); - if (rcu_segcblist_is_offloaded(&my_rdp->cblist)) { + if (rcu_rdp_is_offloaded(my_rdp)) { raw_spin_unlock_rcu_node(my_rnp); /* irqs remain disabled. */ __call_rcu_nocb_wake(my_rdp, true, flags); } else { diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 2d60377..cd513ea 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -16,8 +16,70 @@ #ifdef CONFIG_RCU_NOCB_CPU static cpumask_var_t rcu_nocb_mask; /* CPUs to have callbacks offloaded. */ static bool __read_mostly rcu_nocb_poll; /* Offload kthread are to poll. */ +static inline int rcu_lockdep_is_held_nocb(struct rcu_data *rdp) +{ + return lockdep_is_held(&rdp->nocb_lock); +} + +static inline bool rcu_current_is_nocb_kthread(struct rcu_data *rdp) +{ + /* Race on early boot between thread creation and assignment */ + if (!rdp->nocb_cb_kthread || !rdp->nocb_gp_kthread) + return true; + + if (current == rdp->nocb_cb_kthread || current == rdp->nocb_gp_kthread) + if (in_task()) + return true; + return false; +} + +static inline bool rcu_running_nocb_timer(struct rcu_data *rdp) +{ + return (timer_curr_running(&rdp->nocb_timer) && !in_irq()); +} +#else +static inline int rcu_lockdep_is_held_nocb(struct rcu_data *rdp) +{ + return 0; +} + +static inline bool rcu_current_is_nocb_kthread(struct rcu_data *rdp) +{ + return false; +} + +static inline bool rcu_running_nocb_timer(struct rcu_data *rdp) +{ + return false; +} + #endif /* #ifdef CONFIG_RCU_NOCB_CPU */ +static bool rcu_rdp_is_offloaded(struct rcu_data *rdp) +{ + /* + * In order to read the offloaded state of an rdp is a safe + * and stable way and prevent from its value to be changed + * under us, we must either hold the barrier mutex, the cpu + * hotplug lock (read or write) or the nocb lock. Local + * non-preemptible reads are also safe. NOCB kthreads and + * timers have their own means of synchronization against the + * offloaded state updaters. + */ + RCU_LOCKDEP_WARN( + !(lockdep_is_held(&rcu_state.barrier_mutex) || + (IS_ENABLED(CONFIG_HOTPLUG_CPU) && lockdep_is_cpus_held()) || + rcu_lockdep_is_held_nocb(rdp) || + (rdp == this_cpu_ptr(&rcu_data) && + !(IS_ENABLED(CONFIG_PREEMPT_COUNT) && preemptible())) || + rcu_current_is_nocb_kthread(rdp) || + rcu_running_nocb_timer(rdp)), + "Unsafe read of RCU_NOCB offloaded state" + ); + + return rcu_segcblist_is_offloaded(&rdp->cblist); +} + /* * Check the RCU kernel configuration parameters and print informative * messages about anything out of the ordinary. @@ -1257,7 +1319,7 @@ int rcu_needs_cpu(u64 basemono, u64 *nextevt) { *nextevt = KTIME_MAX; return !rcu_segcblist_empty(&this_cpu_ptr(&rcu_data)->cblist) && - !rcu_segcblist_is_offloaded(&this_cpu_ptr(&rcu_data)->cblist); + !rcu_rdp_is_offloaded(this_cpu_ptr(&rcu_data)); } /* @@ -1352,7 +1414,7 @@ int rcu_needs_cpu(u64 basemono, u64 *nextevt) /* If no non-offloaded callbacks, RCU doesn't need the CPU. */ if (rcu_segcblist_empty(&rdp->cblist) || - rcu_segcblist_is_offloaded(&this_cpu_ptr(&rcu_data)->cblist)) { + rcu_rdp_is_offloaded(rdp)) { *nextevt = KTIME_MAX; return 0; } @@ -1388,7 +1450,7 @@ static void rcu_prepare_for_idle(void) int tne; lockdep_assert_irqs_disabled(); - if (rcu_segcblist_is_offloaded(&rdp->cblist)) + if (rcu_rdp_is_offloaded(rdp)) return; /* Handle nohz enablement switches conservatively. */ @@ -1429,7 +1491,7 @@ static void rcu_cleanup_after_idle(void) struct rcu_data *rdp = this_cpu_ptr(&rcu_data); lockdep_assert_irqs_disabled(); - if (rcu_segcblist_is_offloaded(&rdp->cblist)) + if (rcu_rdp_is_offloaded(rdp)) return; if (rcu_try_advance_all_cbs()) invoke_rcu_core(); @@ -1560,7 +1622,7 @@ static void rcu_nocb_bypass_unlock(struct rcu_data *rdp) static void rcu_nocb_lock(struct rcu_data *rdp) { lockdep_assert_irqs_disabled(); - if (!rcu_segcblist_is_offloaded(&rdp->cblist)) + if (!rcu_rdp_is_offloaded(rdp)) return; raw_spin_lock(&rdp->nocb_lock); } @@ -1571,7 +1633,7 @@ static void rcu_nocb_lock(struct rcu_data *rdp) */ static void rcu_nocb_unlock(struct rcu_data *rdp) { - if (rcu_segcblist_is_offloaded(&rdp->cblist)) { + if (rcu_rdp_is_offloaded(rdp)) { lockdep_assert_irqs_disabled(); raw_spin_unlock(&rdp->nocb_lock); } @@ -1584,7 +1646,7 @@ static void rcu_nocb_unlock(struct rcu_data *rdp) static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp, unsigned long flags) { - if (rcu_segcblist_is_offloaded(&rdp->cblist)) { + if (rcu_rdp_is_offloaded(rdp)) { lockdep_assert_irqs_disabled(); raw_spin_unlock_irqrestore(&rdp->nocb_lock, flags); } else { @@ -1596,7 +1658,7 @@ static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp, static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp) { lockdep_assert_irqs_disabled(); - if (rcu_segcblist_is_offloaded(&rdp->cblist)) + if (rcu_rdp_is_offloaded(rdp)) lockdep_assert_held(&rdp->nocb_lock); } @@ -1690,7 +1752,7 @@ static bool rcu_nocb_do_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp, { struct rcu_cblist rcl; - WARN_ON_ONCE(!rcu_segcblist_is_offloaded(&rdp->cblist)); + WARN_ON_ONCE(!rcu_rdp_is_offloaded(rdp)); rcu_lockdep_assert_cblist_protected(rdp); lockdep_assert_held(&rdp->nocb_bypass_lock); if (rhp && !rcu_cblist_n_cbs(&rdp->nocb_bypass)) { @@ -1718,7 +1780,7 @@ static bool rcu_nocb_do_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp, static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp, unsigned long j) { - if (!rcu_segcblist_is_offloaded(&rdp->cblist)) + if (!rcu_rdp_is_offloaded(rdp)) return true; rcu_lockdep_assert_cblist_protected(rdp); rcu_nocb_bypass_lock(rdp); @@ -1732,7 +1794,7 @@ static bool rcu_nocb_flush_bypass(struct rcu_data *rdp, struct rcu_head *rhp, static void rcu_nocb_try_flush_bypass(struct rcu_data *rdp, unsigned long j) { rcu_lockdep_assert_cblist_protected(rdp); - if (!rcu_segcblist_is_offloaded(&rdp->cblist) || + if (!rcu_rdp_is_offloaded(rdp) || !rcu_nocb_bypass_trylock(rdp)) return; WARN_ON_ONCE(!rcu_nocb_do_flush_bypass(rdp, NULL, j)); @@ -1764,7 +1826,7 @@ static bool rcu_nocb_try_bypass(struct rcu_data *rdp, struct rcu_head *rhp, unsigned long j = jiffies; long ncbs = rcu_cblist_n_cbs(&rdp->nocb_bypass); - if (!rcu_segcblist_is_offloaded(&rdp->cblist)) { + if (!rcu_rdp_is_offloaded(rdp)) { *was_alldone = !rcu_segcblist_pend_cbs(&rdp->cblist); return false; /* Not offloaded, no bypassing. */ } @@ -2397,7 +2459,7 @@ int rcu_nocb_cpu_deoffload(int cpu) } mutex_lock(&rcu_state.barrier_mutex); cpus_read_lock(); - if (rcu_segcblist_is_offloaded(&rdp->cblist)) { + if (rcu_rdp_is_offloaded(rdp)) { if (cpu_online(cpu)) ret = work_on_cpu(cpu, rcu_nocb_rdp_deoffload, rdp); else @@ -2472,7 +2534,7 @@ int rcu_nocb_cpu_offload(int cpu) mutex_lock(&rcu_state.barrier_mutex); cpus_read_lock(); - if (!rcu_segcblist_is_offloaded(&rdp->cblist)) { + if (!rcu_rdp_is_offloaded(rdp)) { if (cpu_online(cpu)) ret = work_on_cpu(cpu, rcu_nocb_rdp_offload, rdp); else -- 2.9.5