mm/init: cpu_hotplug_init() must be initialized before SLAB

SLAB uses get/put_online_cpus() which use a mutex which is itself only
initialized when cpu_hotplug_init() is called.  Currently we hang suring
boot in SLAB due to doing that too late.

Reported by James Bottomley and Sachin Sant (and possibly others).
Debugged by Benjamin Herrenschmidt.

This just removes the dynamic initialization of the data structures, and
replaces it with a static one, avoiding this dependency entirely, and
removing one unnecessary special initcall.

Tested-by: Sachin Sant <sachinp@in.ibm.com>
Tested-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Tested-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 5 insertions, 8 deletions

diff --git a/kernel/cpu.c b/kernel/cpu.c
index 395b6974dc8d..8ce10043e4ac 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -34,14 +34,11 @@ static struct {
          * an ongoing cpu hotplug operation.
          */
         int refcount;
-} cpu_hotplug;
-
-void __init cpu_hotplug_init(void)
-{
-        cpu_hotplug.active_writer = NULL;
-        mutex_init(&cpu_hotplug.lock);
-        cpu_hotplug.refcount = 0;
-}
+} cpu_hotplug = {
+        .active_writer = NULL,
+        .lock = __MUTEX_INITIALIZER(cpu_hotplug.lock),
+        .refcount = 0,
+};
 
 #ifdef CONFIG_HOTPLUG_CPU