Patch "smpboot: Add missing get_online_cpus() in smpboot_register_percpu_thread()" has been added to the 3.18-stable tree

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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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