[PATCH] Make kthread_stop() not oops when passed a bad pointer

[Matthew Wilcox <matthew@wil.cx>]

Due to some botched error handling code in a driver I was writing, I
recently called kthread_stop(NULL).  It's terribly exciting to discover
that you've just oopsed while holding a mutex that's required in order
to shut down.  Make kthread_stop a little more robust against numbskulls
like me.

Signed-off-by: Matthew Wilcox <willy@linux.intel.com>

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 96cff2f..06c3477 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -201,6 +201,9 @@ int kthread_stop(struct task_struct *k)
 {
 	int ret;
 
+	if (!k || IS_ERR(k))
+		return -EINVAL;
+
 	mutex_lock(&kthread_stop_lock);
 
 	/* It could exit after stop_info.k set, but before wake_up_process. */
-- 
Intel are signing my paycheques ... these opinions are still mine
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
a retrograde step."