Signed-off-by: Jason Wessel <jason.wessel@windriver.com>

---
 kernel/kgdb.c |   18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

--- a/kernel/kgdb.c
+++ b/kernel/kgdb.c
@@ -121,6 +121,7 @@ struct task_struct *kgdb_usethread, *kgd
 
 int debugger_step;
 atomic_t debugger_active;
+static atomic_t kgdb_sync = ATOMIC_INIT(-1);
 
 /* Our I/O buffers. */
 static char remcom_in_buffer[BUFMAX];
@@ -638,8 +639,14 @@ static void kgdb_wait(struct pt_regs *re
 	kgdb_info[processor].task = current;
 	atomic_set(&procindebug[processor], 1);
 
+	/* The master processor must be active to enter here, but this is
+	 * gaurd in case the master processor had not been selected if
+	 * this was an entry via nmi.
+	 */
+	while (!atomic_read(&debugger_active));
+
 	/* Wait till master processor goes completely into the debugger.
-	 * FIXME: this looks racy */
+	 */
 	while (!atomic_read(&procindebug[atomic_read(&debugger_active) - 1])) {
 		int i = 10;	/* an arbitrary number */
 
@@ -973,8 +980,13 @@ int kgdb_handle_exception(int ex_vector,
 	/* Hold debugger_active */
 	procid = raw_smp_processor_id();
 
-	while (cmpxchg(&atomic_read(&debugger_active), 0, (procid + 1)) != 0) {
+	while (1) {
 		int i = 25;	/* an arbitrary number */
+		if (atomic_read(&kgdb_sync) < 0 &&
+			atomic_inc_and_test(&kgdb_sync)) {
+			atomic_set(&debugger_active, procid + 1);
+			break;
+		}
 
 		while (--i)
 			cpu_relax();
@@ -991,6 +1003,7 @@ int kgdb_handle_exception(int ex_vector,
 	if (atomic_read(&cpu_doing_single_step) != -1 &&
 	    atomic_read(&cpu_doing_single_step) != procid) {
 		atomic_set(&debugger_active, 0);
+		atomic_set(&kgdb_sync, -1);
 		clocksource_touch_watchdog();
 		kgdb_softlock_skip[procid] = 1;
 		local_irq_restore(flags);
@@ -1557,6 +1570,7 @@ int kgdb_handle_exception(int ex_vector,
  kgdb_restore:
 	/* Free debugger_active */
 	atomic_set(&debugger_active, 0);
+	atomic_set(&kgdb_sync, -1);
 	clocksource_touch_watchdog();
 	kgdb_softlock_skip[processor] = 1;
 	local_irq_restore(flags);