From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3wshnZ65fVzDql0 for ; Wed, 21 Jun 2017 08:08:50 +1000 (AEST) Received: from pps.filterd (m0098416.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.20/8.16.0.20) with SMTP id v5KM8j5A066618 for ; Tue, 20 Jun 2017 18:08:48 -0400 Received: from e24smtp05.br.ibm.com (e24smtp05.br.ibm.com [32.104.18.26]) by mx0b-001b2d01.pphosted.com with ESMTP id 2b6rv1tmrq-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Tue, 20 Jun 2017 18:08:47 -0400 Received: from localhost by e24smtp05.br.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Tue, 20 Jun 2017 19:08:46 -0300 Received: from d24av05.br.ibm.com (d24av05.br.ibm.com [9.18.232.44]) by d24relay02.br.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id v5KM8hRm8061408 for ; Tue, 20 Jun 2017 19:08:43 -0300 Received: from d24av05.br.ibm.com (localhost [127.0.0.1]) by d24av05.br.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id v5KJ8hjF032476 for ; Tue, 20 Jun 2017 16:08:44 -0300 From: Thiago Jung Bauermann To: linuxppc-dev@lists.ozlabs.org Cc: linux-kernel@vger.kernel.org, Thomas Gleixner , Michael Bringmann , Nathan Fontenot , John Allen , Thiago Jung Bauermann Subject: [PATCH] powerpc: Only obtain cpu_hotplug_lock if called by rtasd Date: Tue, 20 Jun 2017 19:08:30 -0300 Message-Id: <1497996510-4032-1-git-send-email-bauerman@linux.vnet.ibm.com> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Calling arch_update_cpu_topology from a CPU hotplug state machine callback hits a deadlock because the function tries to get a read lock on cpu_hotplug_lock while the state machine still holds a write lock on it. Since all callers of arch_update_cpu_topology except rtasd already hold cpu_hotplug_lock, this patch changes the function to use stop_machine_cpuslocked and creates a separate function for rtasd which still tries to obtain the lock. Michael Bringmann investigated the bug and provided a detailed analysis of the deadlock on this previous RFC for an alternate solution: https://patchwork.ozlabs.org/patch/771293/ Signed-off-by: Thiago Jung Bauermann --- Notes: This patch applies on tip/smp/hotplug, it should probably be carried there. arch/powerpc/include/asm/topology.h | 6 ++++++ arch/powerpc/kernel/rtasd.c | 2 +- arch/powerpc/mm/numa.c | 22 +++++++++++++++++++--- 3 files changed, 26 insertions(+), 4 deletions(-) diff --git a/arch/powerpc/include/asm/topology.h b/arch/powerpc/include/asm/topology.h index 8b3b46b7b0f2..a2d36b7703ae 100644 --- a/arch/powerpc/include/asm/topology.h +++ b/arch/powerpc/include/asm/topology.h @@ -43,6 +43,7 @@ extern void __init dump_numa_cpu_topology(void); extern int sysfs_add_device_to_node(struct device *dev, int nid); extern void sysfs_remove_device_from_node(struct device *dev, int nid); +extern int numa_update_cpu_topology(bool cpus_locked); #else @@ -57,6 +58,11 @@ static inline void sysfs_remove_device_from_node(struct device *dev, int nid) { } + +static inline int numa_update_cpu_topology(bool cpus_locked) +{ + return 0; +} #endif /* CONFIG_NUMA */ #if defined(CONFIG_NUMA) && defined(CONFIG_PPC_SPLPAR) diff --git a/arch/powerpc/kernel/rtasd.c b/arch/powerpc/kernel/rtasd.c index 3650732639ed..0f0b1b2f3b60 100644 --- a/arch/powerpc/kernel/rtasd.c +++ b/arch/powerpc/kernel/rtasd.c @@ -283,7 +283,7 @@ static void prrn_work_fn(struct work_struct *work) * the RTAS event. */ pseries_devicetree_update(-prrn_update_scope); - arch_update_cpu_topology(); + numa_update_cpu_topology(false); } static DECLARE_WORK(prrn_work, prrn_work_fn); diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c index 371792e4418f..b95c584ce19d 100644 --- a/arch/powerpc/mm/numa.c +++ b/arch/powerpc/mm/numa.c @@ -1311,8 +1311,10 @@ static int update_lookup_table(void *data) /* * Update the node maps and sysfs entries for each cpu whose home node * has changed. Returns 1 when the topology has changed, and 0 otherwise. + * + * cpus_locked says whether we already hold cpu_hotplug_lock. */ -int arch_update_cpu_topology(void) +int numa_update_cpu_topology(bool cpus_locked) { unsigned int cpu, sibling, changed = 0; struct topology_update_data *updates, *ud; @@ -1400,15 +1402,23 @@ int arch_update_cpu_topology(void) if (!cpumask_weight(&updated_cpus)) goto out; - stop_machine(update_cpu_topology, &updates[0], &updated_cpus); + if (cpus_locked) + stop_machine_cpuslocked(update_cpu_topology, &updates[0], + &updated_cpus); + else + stop_machine(update_cpu_topology, &updates[0], &updated_cpus); /* * Update the numa-cpu lookup table with the new mappings, even for * offline CPUs. It is best to perform this update from the stop- * machine context. */ - stop_machine(update_lookup_table, &updates[0], + if (cpus_locked) + stop_machine_cpuslocked(update_lookup_table, &updates[0], cpumask_of(raw_smp_processor_id())); + else + stop_machine(update_lookup_table, &updates[0], + cpumask_of(raw_smp_processor_id())); for (ud = &updates[0]; ud; ud = ud->next) { unregister_cpu_under_node(ud->cpu, ud->old_nid); @@ -1426,6 +1436,12 @@ int arch_update_cpu_topology(void) return changed; } +int arch_update_cpu_topology(void) +{ + lockdep_assert_cpus_held(); + return numa_update_cpu_topology(true); +} + static void topology_work_fn(struct work_struct *work) { rebuild_sched_domains(); -- 2.7.4