mm, percpu: Make sure percpu_alloc early parameter has an argument

Otherwise we are getting a nil dereference if percpu_alloc kernel boot
argument is specified without value.

 | [    0.000000] BUG: unable to handle kernel NULL pointer dereference at           (null)
 | [    0.000000] IP: [<ffffffff81391360>] strcmp+0x10/0x30

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Tejun Heo <tj@kernel.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/mm/percpu.c b/mm/percpu.c
index ec2589616e7d..8c8e08f3a692 100644
--- a/mm/percpu.c
+++ b/mm/percpu.c
@@ -1380,6 +1380,9 @@ enum pcpu_fc pcpu_chosen_fc __initdata = PCPU_FC_AUTO;
 
 static int __init percpu_alloc_setup(char *str)
 {
+        if (!str)
+                return -EINVAL;
+
         if (0)
                 /* nada */;
 #ifdef CONFIG_NEED_PER_CPU_EMBED_FIRST_CHUNK