From 677616e3ecaa43e77a81e36aa162d32bdba01476 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() commit 4bee96860a65c3a62d332edac331b3cf936ba3ad upstream. 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 Link: http://lkml.kernel.org/r/1406777421-12830-1-git-send-email-laijs@cn.fujitsu.com Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman --- kernel/smpboot.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/kernel/smpboot.c b/kernel/smpboot.c index 02fc5c93367..7020eecb398 100644 --- a/kernel/smpboot.c +++ b/kernel/smpboot.c @@ -279,6 +279,7 @@ 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); @@ -291,6 +292,7 @@ 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); -- 2.11.0