[PATCH 3.18 36/39] smpboot: Add missing get_online_cpus() in smpboot_register_percpu_thread()

From: Greg Kroah-Hartman
Date: Mon Feb 09 2015 - 03:44:55 EST


3.18-stable review patch. If anyone has any objections, please let me know.

------------------

From: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>

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: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
kernel/smpboot.c | 2 ++
1 file changed, 2 insertions(+)

--- a/kernel/smpboot.c
+++ b/kernel/smpboot.c
@@ -279,6 +279,7 @@ int smpboot_register_percpu_thread(struc
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(struc
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);


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/