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[];