From 4bee96860a65c3a62d332edac331b3cf936ba3ad Mon Sep 17 00:00:00 2001 From: Lai Jiangshan Date: Thu, 31 Jul 2014 11:30:17 +0800 Subject: [PATCH] smpboot: Add missing get_online_cpus() in smpboot_register_percpu_thread() The following race exists in the smpboot percpu threads management: CPU0 CPU1 cpu_up(2) get_online_cpus(); smpboot_create_threads(2); smpboot_register_percpu_thread(); for_each_online_cpu(); __smpboot_create_thread(); __cpu_up(2); This results in a missing per cpu thread for the newly onlined cpu2 and in a NULL pointer dereference on a consecutive offline of that cpu. Proctect smpboot_register_percpu_thread() with get_online_cpus() to prevent that. [ tglx: Massaged changelog and removed the change in smpboot_unregister_percpu_thread() because that's an optimization and therefor not stable material. ] Signed-off-by: Lai Jiangshan Cc: Thomas Gleixner Cc: Rusty Russell Cc: Peter Zijlstra Cc: Srivatsa S. Bhat Cc: David Rientjes Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/1406777421-12830-1-git-send-email-laijs@cn.fujitsu.com Signed-off-by: Thomas Gleixner --- kernel/smpboot.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/smpboot.c b/kernel/smpboot.c index f032fb5284e3..40190f28db35 100644 --- a/kernel/smpboot.c +++ b/kernel/smpboot.c @@ -280,6 +280,7 @@ int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread) unsigned int cpu; int ret = 0; + get_online_cpus(); mutex_lock(&smpboot_threads_lock); for_each_online_cpu(cpu) { ret = __smpboot_create_thread(plug_thread, cpu); @@ -292,6 +293,7 @@ int smpboot_register_percpu_thread(struct smp_hotplug_thread *plug_thread) list_add(&plug_thread->list, &hotplug_threads); out: mutex_unlock(&smpboot_threads_lock); + put_online_cpus(); return ret; } EXPORT_SYMBOL_GPL(smpboot_register_percpu_thread);