From: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Link: http://lkml.kernel.org/r/1406777421-12830-1-git-send-email-laijs@xxxxxxxxxxxxxx
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
---
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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