3 files changed, 95 insertions, 10 deletions

diff --git a/arch/x86/kernel/kgdb.c b/arch/x86/kernel/kgdb.c
index 62bea7307eaa..bfba6019d762 100644
--- a/arch/x86/kernel/kgdb.c
+++ b/arch/x86/kernel/kgdb.c
@@ -239,6 +239,49 @@ static void kgdb_correct_hw_break(void)
         hw_breakpoint_restore();
 }
 
+static int hw_break_reserve_slot(int breakno)
+{
+        int cpu;
+        int cnt = 0;
+        struct perf_event **pevent;
+
+        for_each_online_cpu(cpu) {
+                cnt++;
+                pevent = per_cpu_ptr(breakinfo[breakno].pev, cpu);
+                if (dbg_reserve_bp_slot(*pevent))
+                        goto fail;
+        }
+
+        return 0;
+
+fail:
+        for_each_online_cpu(cpu) {
+                cnt--;
+                if (!cnt)
+                        break;
+                pevent = per_cpu_ptr(breakinfo[breakno].pev, cpu);
+                dbg_release_bp_slot(*pevent);
+        }
+        return -1;
+}
+
+static int hw_break_release_slot(int breakno)
+{
+        struct perf_event **pevent;
+        int cpu;
+
+        for_each_online_cpu(cpu) {
+                pevent = per_cpu_ptr(breakinfo[breakno].pev, cpu);
+                if (dbg_release_bp_slot(*pevent))
+                        /*
+                         * The debugger is responisble for handing the retry on
+                         * remove failure.
+                         */
+                        return -1;
+        }
+        return 0;
+}
+
 static int
 kgdb_remove_hw_break(unsigned long addr, int len, enum kgdb_bptype bptype)
 {
@@ -250,6 +293,10 @@ kgdb_remove_hw_break(unsigned long addr, int len, enum kgdb_bptype bptype)
         if (i == 4)
                 return -1;
 
+        if (hw_break_release_slot(i)) {
+                printk(KERN_ERR "Cannot remove hw breakpoint at %lx\n", addr);
+                return -1;
+        }
         breakinfo[i].enabled = 0;
 
         return 0;
@@ -316,6 +363,10 @@ kgdb_set_hw_break(unsigned long addr, int len, enum kgdb_bptype bptype)
                 return -1;
         }
         breakinfo[i].addr = addr;
+        if (hw_break_reserve_slot(i)) {
+                breakinfo[i].addr = 0;
+                return -1;
+        }
         breakinfo[i].enabled = 1;
 
         return 0;
diff --git a/include/linux/hw_breakpoint.h b/include/linux/hw_breakpoint.h
index 41235c93e4e9..070ba0621738 100644
--- a/include/linux/hw_breakpoint.h
+++ b/include/linux/hw_breakpoint.h
@@ -75,6 +75,8 @@ extern int __register_perf_hw_breakpoint(struct perf_event *bp);
 extern void unregister_hw_breakpoint(struct perf_event *bp);
 extern void unregister_wide_hw_breakpoint(struct perf_event **cpu_events);
 
+extern int dbg_reserve_bp_slot(struct perf_event *bp);
+extern int dbg_release_bp_slot(struct perf_event *bp);
 extern int reserve_bp_slot(struct perf_event *bp);
 extern void release_bp_slot(struct perf_event *bp);
 
diff --git a/kernel/hw_breakpoint.c b/kernel/hw_breakpoint.c
index c030ae657f20..8a5c7d55ac9f 100644
--- a/kernel/hw_breakpoint.c
+++ b/kernel/hw_breakpoint.c
@@ -243,38 +243,70 @@ static void toggle_bp_slot(struct perf_event *bp, bool enable)
  *       ((per_cpu(nr_bp_flexible, *) > 1) + max(per_cpu(nr_cpu_bp_pinned, *))
  *            + max(per_cpu(nr_task_bp_pinned, *))) < HBP_NUM
  */
-int reserve_bp_slot(struct perf_event *bp)
+static int __reserve_bp_slot(struct perf_event *bp)
 {
         struct bp_busy_slots slots = {0};
-        int ret = 0;
-
-        mutex_lock(&nr_bp_mutex);
 
         fetch_bp_busy_slots(&slots, bp);
 
         /* Flexible counters need to keep at least one slot */
-        if (slots.pinned + (!!slots.flexible) == HBP_NUM) {
-                ret = -ENOSPC;
-                goto end;
-        }
+        if (slots.pinned + (!!slots.flexible) == HBP_NUM)
+                return -ENOSPC;
 
         toggle_bp_slot(bp, true);
 
-end:
+        return 0;
+}
+
+int reserve_bp_slot(struct perf_event *bp)
+{
+        int ret;
+
+        mutex_lock(&nr_bp_mutex);
+
+        ret = __reserve_bp_slot(bp);
+
         mutex_unlock(&nr_bp_mutex);
 
         return ret;
 }
 
+static void __release_bp_slot(struct perf_event *bp)
+{
+        toggle_bp_slot(bp, false);
+}
+
 void release_bp_slot(struct perf_event *bp)
 {
         mutex_lock(&nr_bp_mutex);
 
-        toggle_bp_slot(bp, false);
+        __release_bp_slot(bp);
 
         mutex_unlock(&nr_bp_mutex);
 }
 
+/*
+ * Allow the kernel debugger to reserve breakpoint slots without
+ * taking a lock using the dbg_* variant of for the reserve and
+ * release breakpoint slots.
+ */
+int dbg_reserve_bp_slot(struct perf_event *bp)
+{
+        if (mutex_is_locked(&nr_bp_mutex))
+                return -1;
+
+        return __reserve_bp_slot(bp);
+}
+
+int dbg_release_bp_slot(struct perf_event *bp)
+{
+        if (mutex_is_locked(&nr_bp_mutex))
+                return -1;
+
+        __release_bp_slot(bp);
+
+        return 0;
+}
 
 int register_perf_hw_breakpoint(struct perf_event *bp)
 {