From f4edbcd5d1f350b90583c8f3e0e7112b28f65e62 Mon Sep 17 00:00:00 2001 From: "Srivatsa S. Bhat" Date: Tue, 11 Mar 2014 02:05:58 +0530 Subject: [PATCH] s390, smp: Fix CPU hotplug callback registration Subsystems that want to register CPU hotplug callbacks, as well as perform initialization for the CPUs that are already online, often do it as shown below: get_online_cpus(); for_each_online_cpu(cpu) init_cpu(cpu); register_cpu_notifier(&foobar_cpu_notifier); put_online_cpus(); This is wrong, since it is prone to ABBA deadlocks involving the cpu_add_remove_lock and the cpu_hotplug.lock (when running concurrently with CPU hotplug operations). Instead, the correct and race-free way of performing the callback registration is: cpu_notifier_register_begin(); for_each_online_cpu(cpu) init_cpu(cpu); /* Note the use of the double underscored version of the API */ __register_cpu_notifier(&foobar_cpu_notifier); cpu_notifier_register_done(); Fix the smp code in s390 by using this latter form of callback registration. Cc: Martin Schwidefsky Cc: Heiko Carstens Cc: Thomas Gleixner Cc: Ingo Molnar Signed-off-by: Srivatsa S. Bhat Signed-off-by: Rafael J. Wysocki --- arch/s390/kernel/smp.c | 13 +++++++++---- 1 file changed, 9 insertions(+), 4 deletions(-) diff --git a/arch/s390/kernel/smp.c b/arch/s390/kernel/smp.c index a7125b62a9a6..e10be3541816 100644 --- a/arch/s390/kernel/smp.c +++ b/arch/s390/kernel/smp.c @@ -1057,19 +1057,24 @@ static DEVICE_ATTR(rescan, 0200, NULL, rescan_store); static int __init s390_smp_init(void) { - int cpu, rc; + int cpu, rc = 0; - hotcpu_notifier(smp_cpu_notify, 0); #ifdef CONFIG_HOTPLUG_CPU rc = device_create_file(cpu_subsys.dev_root, &dev_attr_rescan); if (rc) return rc; #endif + cpu_notifier_register_begin(); for_each_present_cpu(cpu) { rc = smp_add_present_cpu(cpu); if (rc) - return rc; + goto out; } - return 0; + + __hotcpu_notifier(smp_cpu_notify, 0); + +out: + cpu_notifier_register_done(); + return rc; } subsys_initcall(s390_smp_init); -- 2.39.2