2 files changed, 56 insertions, 50 deletions

diff --git a/kernel/debug/debug_core.c b/kernel/debug/debug_core.c
index bb9497724808..26dbdc37d219 100644
--- a/kernel/debug/debug_core.c
+++ b/kernel/debug/debug_core.c
@@ -110,13 +110,15 @@ static struct kgdb_bkpt		kgdb_break[KGDB_MAX_BREAKPOINTS] = {
  */
 atomic_t			kgdb_active = ATOMIC_INIT(-1);
 EXPORT_SYMBOL_GPL(kgdb_active);
+static DEFINE_RAW_SPINLOCK(dbg_master_lock);
+static DEFINE_RAW_SPINLOCK(dbg_slave_lock);
 
 /*
  * We use NR_CPUs not PERCPU, in case kgdb is used to debug early
  * bootup code (which might not have percpu set up yet):
  */
-static atomic_t			passive_cpu_wait[NR_CPUS];
-static atomic_t			cpu_in_kgdb[NR_CPUS];
+static atomic_t			masters_in_kgdb;
+static atomic_t			slaves_in_kgdb;
 static atomic_t			kgdb_break_tasklet_var;
 atomic_t			kgdb_setting_breakpoint;
 
@@ -478,14 +480,23 @@ static void dbg_touch_watchdogs(void)
 	rcu_cpu_stall_reset();
 }
 
-static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs)
+static int kgdb_cpu_enter(struct kgdb_state *ks, struct pt_regs *regs,
+		int exception_state)
 {
 	unsigned long flags;
 	int sstep_tries = 100;
 	int error;
-	int i, cpu;
+	int cpu;
 	int trace_on = 0;
+	int online_cpus = num_online_cpus();
 
+	kgdb_info[ks->cpu].enter_kgdb++;
+	kgdb_info[ks->cpu].exception_state |= exception_state;
+
+	if (exception_state == DCPU_WANT_MASTER)
+		atomic_inc(&masters_in_kgdb);
+	else
+		atomic_inc(&slaves_in_kgdb);
 	kgdb_disable_hw_debug(ks->linux_regs);
 
 acquirelock:
@@ -500,14 +511,15 @@ acquirelock:
 	kgdb_info[cpu].task = current;
 	kgdb_info[cpu].ret_state = 0;
 	kgdb_info[cpu].irq_depth = hardirq_count() >> HARDIRQ_SHIFT;
-	/*
-	 * Make sure the above info reaches the primary CPU before
-	 * our cpu_in_kgdb[] flag setting does:
-	 */
-	atomic_inc(&cpu_in_kgdb[cpu]);
 
-	if (exception_level == 1)
+	/* Make sure the above info reaches the primary CPU */
+	smp_mb();
+
+	if (exception_level == 1) {
+		if (raw_spin_trylock(&dbg_master_lock))
+			atomic_xchg(&kgdb_active, cpu);
 		goto cpu_master_loop;
+	}
 
 	/*
 	 * CPU will loop if it is a slave or request to become a kgdb
@@ -519,10 +531,12 @@ cpu_loop:
 			kgdb_info[cpu].exception_state &= ~DCPU_NEXT_MASTER;
 			goto cpu_master_loop;
 		} else if (kgdb_info[cpu].exception_state & DCPU_WANT_MASTER) {
-			if (atomic_cmpxchg(&kgdb_active, -1, cpu) == cpu)
+			if (raw_spin_trylock(&dbg_master_lock)) {
+				atomic_xchg(&kgdb_active, cpu);
 				break;
+			}
 		} else if (kgdb_info[cpu].exception_state & DCPU_IS_SLAVE) {
-			if (!atomic_read(&passive_cpu_wait[cpu]))
+			if (!raw_spin_is_locked(&dbg_slave_lock))
 				goto return_normal;
 		} else {
 return_normal:
@@ -533,7 +547,11 @@ return_normal:
 				arch_kgdb_ops.correct_hw_break();
 			if (trace_on)
 				tracing_on();
-			atomic_dec(&cpu_in_kgdb[cpu]);
+			kgdb_info[cpu].exception_state &=
+				~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
+			kgdb_info[cpu].enter_kgdb--;
+			smp_mb__before_atomic_dec();
+			atomic_dec(&slaves_in_kgdb);
 			dbg_touch_watchdogs();
 			local_irq_restore(flags);
 			return 0;
@@ -551,6 +569,7 @@ return_normal:
 	    (kgdb_info[cpu].task &&
 	     kgdb_info[cpu].task->pid != kgdb_sstep_pid) && --sstep_tries) {
 		atomic_set(&kgdb_active, -1);
+		raw_spin_unlock(&dbg_master_lock);
 		dbg_touch_watchdogs();
 		local_irq_restore(flags);
 
@@ -576,10 +595,8 @@ return_normal:
 	 * Get the passive CPU lock which will hold all the non-primary
 	 * CPU in a spin state while the debugger is active
 	 */
-	if (!kgdb_single_step) {
-		for (i = 0; i < NR_CPUS; i++)
-			atomic_inc(&passive_cpu_wait[i]);
-	}
+	if (!kgdb_single_step)
+		raw_spin_lock(&dbg_slave_lock);
 
 #ifdef CONFIG_SMP
 	/* Signal the other CPUs to enter kgdb_wait() */
@@ -590,10 +607,9 @@ return_normal:
 	/*
 	 * Wait for the other CPUs to be notified and be waiting for us:
 	 */
-	for_each_online_cpu(i) {
-		while (kgdb_do_roundup && !atomic_read(&cpu_in_kgdb[i]))
-			cpu_relax();
-	}
+	while (kgdb_do_roundup && (atomic_read(&masters_in_kgdb) +
+				atomic_read(&slaves_in_kgdb)) != online_cpus)
+		cpu_relax();
 
 	/*
 	 * At this point the primary processor is completely
@@ -634,24 +650,11 @@ cpu_master_loop:
 	if (dbg_io_ops->post_exception)
 		dbg_io_ops->post_exception();
 
-	atomic_dec(&cpu_in_kgdb[ks->cpu]);
-
 	if (!kgdb_single_step) {
-		for (i = NR_CPUS-1; i >= 0; i--)
-			atomic_dec(&passive_cpu_wait[i]);
-		/*
-		 * Wait till all the CPUs have quit from the debugger,
-		 * but allow a CPU that hit an exception and is
-		 * waiting to become the master to remain in the debug
-		 * core.
-		 */
-		for_each_online_cpu(i) {
-			while (kgdb_do_roundup &&
-			       atomic_read(&cpu_in_kgdb[i]) &&
-			       !(kgdb_info[i].exception_state &
-				 DCPU_WANT_MASTER))
-				cpu_relax();
-		}
+		raw_spin_unlock(&dbg_slave_lock);
+		/* Wait till all the CPUs have quit from the debugger. */
+		while (kgdb_do_roundup && atomic_read(&slaves_in_kgdb))
+			cpu_relax();
 	}
 
 kgdb_restore:
@@ -666,8 +669,15 @@ kgdb_restore:
 		arch_kgdb_ops.correct_hw_break();
 	if (trace_on)
 		tracing_on();
+
+	kgdb_info[cpu].exception_state &=
+		~(DCPU_WANT_MASTER | DCPU_IS_SLAVE);
+	kgdb_info[cpu].enter_kgdb--;
+	smp_mb__before_atomic_dec();
+	atomic_dec(&masters_in_kgdb);
 	/* Free kgdb_active */
 	atomic_set(&kgdb_active, -1);
+	raw_spin_unlock(&dbg_master_lock);
 	dbg_touch_watchdogs();
 	local_irq_restore(flags);
 
@@ -686,7 +696,6 @@ kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
 {
 	struct kgdb_state kgdb_var;
 	struct kgdb_state *ks = &kgdb_var;
-	int ret;
 
 	ks->cpu			= raw_smp_processor_id();
 	ks->ex_vector		= evector;
@@ -697,11 +706,10 @@ kgdb_handle_exception(int evector, int signo, int ecode, struct pt_regs *regs)
 
 	if (kgdb_reenter_check(ks))
 		return 0; /* Ouch, double exception ! */
-	kgdb_info[ks->cpu].exception_state |= DCPU_WANT_MASTER;
-	ret = kgdb_cpu_enter(ks, regs);
-	kgdb_info[ks->cpu].exception_state &= ~(DCPU_WANT_MASTER |
-						DCPU_IS_SLAVE);
-	return ret;
+	if (kgdb_info[ks->cpu].enter_kgdb != 0)
+		return 0;
+
+	return kgdb_cpu_enter(ks, regs, DCPU_WANT_MASTER);
 }
 
 int kgdb_nmicallback(int cpu, void *regs)
@@ -714,12 +722,9 @@ int kgdb_nmicallback(int cpu, void *regs)
 	ks->cpu			= cpu;
 	ks->linux_regs		= regs;
 
-	if (!atomic_read(&cpu_in_kgdb[cpu]) &&
-	    atomic_read(&kgdb_active) != -1 &&
-	    atomic_read(&kgdb_active) != cpu) {
-		kgdb_info[cpu].exception_state |= DCPU_IS_SLAVE;
-		kgdb_cpu_enter(ks, regs);
-		kgdb_info[cpu].exception_state &= ~DCPU_IS_SLAVE;
+	if (kgdb_info[ks->cpu].enter_kgdb == 0 &&
+			raw_spin_is_locked(&dbg_master_lock)) {
+		kgdb_cpu_enter(ks, regs, DCPU_IS_SLAVE);
 		return 0;
 	}
 #endif
diff --git a/kernel/debug/debug_core.h b/kernel/debug/debug_core.h
index c5d753d80f67..3494c28a7e7a 100644
--- a/kernel/debug/debug_core.h
+++ b/kernel/debug/debug_core.h
@@ -40,6 +40,7 @@ struct debuggerinfo_struct {
 	int			exception_state;
 	int			ret_state;
 	int			irq_depth;
+	int			enter_kgdb;
 };
 
 extern struct debuggerinfo_struct kgdb_info[];