This is a note to let you know that I've just added the patch titled
smpboot: Add missing get_online_cpus() in smpboot_register_percpu_thread()
to the 3.18-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
smpboot-add-missing-get_online_cpus-in-smpboot_register_percpu_thread.patch
and it can be found in the queue-3.18 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 4bee96860a65c3a62d332edac331b3cf936ba3ad Mon Sep 17 00:00:00 2001
From: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
Date: Thu, 31 Jul 2014 11:30:17 +0800
Subject: smpboot: Add missing get_online_cpus() in smpboot_register_percpu_thread()
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);
Patches currently in stable-queue which might be from laijs@xxxxxxxxxxxxxx are
queue-3.18/smpboot-add-missing-get_online_cpus-in-smpboot_register_percpu_thread.patch
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