[PATCH v3] x86: Fix an RT MCE crash

From: Corey Minyard <redacted>

On some x86 systems an MCE interrupt would come in before the kernel
was ready for it.  Looking at the latest RT code, it has similar
(but not quite the same) code, except it adds a bool that tells if
MCE handling is initialized.  That was required because they had
switched to use swork instead of a kernel thread.  Here, just
checking to see if the thread is NULL is good enough to see if
MCE handling is initialized.

Suggested-by: Borislav Petkov <bp@alien8.de>
Signed-off-by: Corey Minyard <redacted>
---
 arch/x86/kernel/cpu/mcheck/mce.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

Added Suggested-by: for Boris.

diff --git a/arch/x86/kernel/cpu/mcheck/mce.c b/arch/x86/kernel/cpu/mcheck/mce.c
index aaf4b9b..cc70d98 100644
--- a/arch/x86/kernel/cpu/mcheck/mce.c
+++ b/arch/x86/kernel/cpu/mcheck/mce.c

@@ -1391,7 +1391,8 @@ static int mce_notify_work_init(void)
 
 static void mce_notify_work(void)
 {
-	wake_up_process(mce_notify_helper);
+	if (mce_notify_helper)
+		wake_up_process(mce_notify_helper);
 }
 #else
 static void mce_notify_work(void)

-- 
2.7.4