x86, mce: Improve timeout error messages

There are four different possible types of timeouts.  Distinguish
them in the logs to help debug them.

Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Link: http://lkml.kernel.org/r/0fa6d2653a54a01c48b43a3583caf950ea99606e.1419178397.git.luto@amacapital.net
Signed-off-by: Borislav Petkov <bp@suse.de>

arch/x86/kernel/cpu/mcheck/mce.c

@@ -311,7 +311,7 @@ static void wait_for_panic(void)
 	panic("Panicing machine check CPU died");
 }
 
-static void mce_panic(char *msg, struct mce *final, char *exp)
+static void mce_panic(const char *msg, struct mce *final, char *exp)
 {
 	int i, apei_err = 0;
 
@@ -735,7 +735,7 @@ static atomic_t mce_callin;
 /*
  * Check if a timeout waiting for other CPUs happened.
  */
-static int mce_timed_out(u64 *t)
+static int mce_timed_out(u64 *t, const char *msg)
 {
 	/*
 	 * The others already did panic for some reason.
@@ -750,8 +750,7 @@ static int mce_timed_out(u64 *t)
 		goto out;
 	if ((s64)*t < SPINUNIT) {
 		if (mca_cfg.tolerant <= 1)
-			mce_panic("Timeout synchronizing machine check over CPUs",
-				  NULL, NULL);
+			mce_panic(msg, NULL, NULL);
 		cpu_missing = 1;
 		return 1;
 	}
@@ -867,7 +866,8 @@ static int mce_start(int *no_way_out)
 	 * Wait for everyone.
 	 */
 	while (atomic_read(&mce_callin) != cpus) {
-		if (mce_timed_out(&timeout)) {
+		if (mce_timed_out(&timeout,
+				  "Timeout: Not all CPUs entered broadcast exception handler")) {
 			atomic_set(&global_nwo, 0);
 			return -1;
 		}
@@ -892,7 +892,8 @@ static int mce_start(int *no_way_out)
 		 * only seen by one CPU before cleared, avoiding duplicates.
 		 */
 		while (atomic_read(&mce_executing) < order) {
-			if (mce_timed_out(&timeout)) {
+			if (mce_timed_out(&timeout,
+					  "Timeout: Subject CPUs unable to finish machine check processing")) {
 				atomic_set(&global_nwo, 0);
 				return -1;
 			}
@@ -936,7 +937,8 @@ static int mce_end(int order)
 		 * loops.
 		 */
 		while (atomic_read(&mce_executing) <= cpus) {
-			if (mce_timed_out(&timeout))
+			if (mce_timed_out(&timeout,
+					  "Timeout: Monarch CPU unable to finish machine check processing"))
 				goto reset;
 			ndelay(SPINUNIT);
 		}
@@ -949,7 +951,8 @@ static int mce_end(int order)
 		 * Subject: Wait for Monarch to finish.
 		 */
 		while (atomic_read(&mce_executing) != 0) {
-			if (mce_timed_out(&timeout))
+			if (mce_timed_out(&timeout,
+					  "Timeout: Monarch CPU did not finish machine check processing"))
 				goto reset;
 			ndelay(SPINUNIT);
 		}