| From | Jiri Slaby <> | Subject | [PATCH 3.12 073/122] smpboot: Add missing get_online_cpus() in smpboot_register_percpu_thread() | Date | Tue, 17 Feb 2015 12:34:20 +0100 |
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From: Lai Jiangshan <laijs@cn.fujitsu.com>
3.12-stable review patch. If anyone has any objections, please let me know.
===============
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 <laijs@cn.fujitsu.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Rusty Russell <rusty@rustcorp.com.au> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com> Cc: David Rientjes <rientjes@google.com> Link: http://lkml.kernel.org/r/1406777421-12830-1-git-send-email-laijs@cn.fujitsu.com Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Jiri Slaby <jslaby@suse.cz> --- kernel/smpboot.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/kernel/smpboot.c b/kernel/smpboot.c index eb89e1807408..60d35ac5d3f1 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); -- 2.2.2
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