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,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 1152CC43461 for ; Wed, 14 Apr 2021 13:24:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id ED8CF61132 for ; Wed, 14 Apr 2021 13:24:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1351332AbhDNNYv (ORCPT ); Wed, 14 Apr 2021 09:24:51 -0400 Received: from mail.kernel.org ([198.145.29.99]:48176 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351466AbhDNNYm (ORCPT ); Wed, 14 Apr 2021 09:24:42 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 254C9611AD; Wed, 14 Apr 2021 13:24:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1618406661; bh=hPfiwarYM7YNO7SIjk41LUb17gc4VW3U0j0edfurSpU=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ps68EAFswVKzvJQ7kUtCj+E/qqxwM831gz3O6gDEd9SvzAiXdhX3VQbnibwpGWuoz y0rXj85A8JGqY+ql3iIK4tUn4zddBtFzkmHoM6+TvfTMZgNUTXOqPHTNibRAwroCQy 0qQDMNmNS89utRQohfdJmuBVg2mytcZ0KllVRBTRdKRD/tGpL+KDLddJrPg6aaQrAX LoMJHK4oJzKUktG0eE08QaJbWdiMsrtU54rRS9Bc06p5eoEsuF9L1ujjKOQwdocrtz DoIoESliDSO1ATzKY0FjdviHbaV+orV82ez6vQgrMcM8yONOKOrduzrrzgGVN+38gA YcIDSUjmvmV8A== From: Frederic Weisbecker To: "Paul E . McKenney" Cc: LKML , Frederic Weisbecker , Uladzislau Rezki , Boqun Feng , Lai Jiangshan , Neeraj Upadhyay , Josh Triplett , Joel Fernandes Subject: [PATCH 1/2] srcu: Fix broken node geometry after early ssp init Date: Wed, 14 Apr 2021 15:24:12 +0200 Message-Id: <20210414132413.98062-2-frederic@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210414132413.98062-1-frederic@kernel.org> References: <20210414132413.98062-1-frederic@kernel.org> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org An ssp initialized before rcu_init_geometry() will have its snp hierarchy based on CONFIG_NR_CPUS. Once rcu_init_geometry() is called, the nodes distribution is shrinked and optimized toward meeting the actual possible number of CPUs detected on boot. Later on, the ssp that was initialized before rcu_init_geometry() is confused and sometimes refers to its initial CONFIG_NR_CPUS based node hierarchy, sometimes to the new num_possible_cpus() based one instead. For example each of its sdp->mynode remain backward and refer to the early node leaves that may not exist anymore. On the other hand the srcu_for_each_node_breadth_first() refers to the new node hierarchy. There are at least two bad possible outcomes to this: 1) a) A callback enqueued early on an sdp is recorded pending on sdp->mynode->srcu_data_have_cbs in srcu_funnel_gp_start() with sdp->mynode pointing to a deep leaf (say 3 levels). b) The grace period ends after rcu_init_geometry() which shrinks the nodes level to a single one. srcu_gp_end() walks through the new snp hierarchy without ever reaching the old leaves so the callback is never executed. This is easily reproduced on an 8 CPUs machine with CONFIG_NR_CPUS >= 32 and "rcupdate.rcu_self_test=1". The srcu_barrier() after early tests verification never completes and the boot hangs: [ 5413.141029] INFO: task swapper/0:1 blocked for more than 4915 seconds. [ 5413.147564] Not tainted 5.12.0-rc4+ #28 [ 5413.151927] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 5413.159753] task:swapper/0 state:D stack: 0 pid: 1 ppid: 0 flags:0x00004000 [ 5413.168099] Call Trace: [ 5413.170555] __schedule+0x36c/0x930 [ 5413.174057] ? wait_for_completion+0x88/0x110 [ 5413.178423] schedule+0x46/0xf0 [ 5413.181575] schedule_timeout+0x284/0x380 [ 5413.185591] ? wait_for_completion+0x88/0x110 [ 5413.189957] ? mark_held_locks+0x61/0x80 [ 5413.193882] ? mark_held_locks+0x61/0x80 [ 5413.197809] ? _raw_spin_unlock_irq+0x24/0x50 [ 5413.202173] ? wait_for_completion+0x88/0x110 [ 5413.206535] wait_for_completion+0xb4/0x110 [ 5413.210724] ? srcu_torture_stats_print+0x110/0x110 [ 5413.215610] srcu_barrier+0x187/0x200 [ 5413.219277] ? rcu_tasks_verify_self_tests+0x50/0x50 [ 5413.224244] ? rdinit_setup+0x2b/0x2b [ 5413.227907] rcu_verify_early_boot_tests+0x2d/0x40 [ 5413.232700] do_one_initcall+0x63/0x310 [ 5413.236541] ? rdinit_setup+0x2b/0x2b [ 5413.240207] ? rcu_read_lock_sched_held+0x52/0x80 [ 5413.244912] kernel_init_freeable+0x253/0x28f [ 5413.249273] ? rest_init+0x250/0x250 [ 5413.252846] kernel_init+0xa/0x110 [ 5413.256257] ret_from_fork+0x22/0x30 2) An ssp that gets initialized before rcu_init_geometry() and used afterward will always have stale rdp->mynode references, resulting in callbacks to be missed in srcu_gp_end(), just like in the previous scenario. Solve this with calling rcu_init_geometry() whenever an struct srcu_state happens to be initialized before rcu_init(). This way we make sure the RCU nodes hierarchy is properly built and distributed before the nodes of a struct srcu_state are allocated. Suggested-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Cc: Boqun Feng Cc: Lai Jiangshan Cc: Neeraj Upadhyay Cc: Josh Triplett Cc: Joel Fernandes Cc: Uladzislau Rezki --- kernel/rcu/rcu.h | 3 +++ kernel/rcu/srcutree.c | 2 ++ kernel/rcu/tree.c | 18 +++++++++++++++++- 3 files changed, 22 insertions(+), 1 deletion(-) diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h index 75ed367d5b60..24db97cbf76b 100644 --- a/kernel/rcu/rcu.h +++ b/kernel/rcu/rcu.h @@ -278,6 +278,7 @@ extern void resched_cpu(int cpu); extern int rcu_num_lvls; extern int num_rcu_lvl[]; extern int rcu_num_nodes; +extern bool rcu_geometry_initialized; static bool rcu_fanout_exact; static int rcu_fanout_leaf; @@ -308,6 +309,8 @@ static inline void rcu_init_levelspread(int *levelspread, const int *levelcnt) } } +extern void rcu_init_geometry(void); + /* Returns a pointer to the first leaf rcu_node structure. */ #define rcu_first_leaf_node() (rcu_state.level[rcu_num_lvls - 1]) diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index 108f9ca06047..05ca3c275af1 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -171,6 +171,8 @@ static int init_srcu_struct_fields(struct srcu_struct *ssp, bool is_static) ssp->sda = alloc_percpu(struct srcu_data); if (!ssp->sda) return -ENOMEM; + if (!rcu_geometry_initialized) + rcu_init_geometry(); init_srcu_struct_nodes(ssp); ssp->srcu_gp_seq_needed_exp = 0; ssp->srcu_last_gp_end = ktime_get_mono_fast_ns(); diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 740f5cd34459..b1d6e60e08d1 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -4556,17 +4556,33 @@ static void __init rcu_init_one(void) } } +bool rcu_geometry_initialized __read_mostly; + /* * Compute the rcu_node tree geometry from kernel parameters. This cannot * replace the definitions in tree.h because those are needed to size * the ->node array in the rcu_state structure. */ -static void __init rcu_init_geometry(void) +void rcu_init_geometry(void) { ulong d; int i; + static unsigned long old_nr_cpu_ids; int rcu_capacity[RCU_NUM_LVLS]; + if (rcu_geometry_initialized) { + /* + * Arrange for warning if rcu_init_geometry() was called before + * setup_nr_cpu_ids(). We may miss cases when + * nr_cpus_ids == NR_CPUS but that shouldn't matter too much. + */ + WARN_ON_ONCE(old_nr_cpu_ids != nr_cpu_ids); + return; + } + + old_nr_cpu_ids = nr_cpu_ids; + rcu_geometry_initialized = true; + /* * Initialize any unspecified boot parameters. * The default values of jiffies_till_first_fqs and -- 2.25.1