1 files changed, 27 insertions, 6 deletions

diff --git a/arch/sh/kernel/unwinder.c b/arch/sh/kernel/unwinder.c
index 2b30fa28b440..b9c122abe251 100644
--- a/arch/sh/kernel/unwinder.c
+++ b/arch/sh/kernel/unwinder.c
@@ -53,8 +53,6 @@ static struct list_head unwinder_list = {
 
 static DEFINE_SPINLOCK(unwinder_lock);
 
-static atomic_t unwinder_running = ATOMIC_INIT(0);
-
 /**
  * select_unwinder - Select the best registered stack unwinder.
  *
@@ -122,6 +120,8 @@ int unwinder_register(struct unwinder *u)
         return ret;
 }
 
+int unwinder_faulted = 0;
+
 /*
  * Unwind the call stack and pass information to the stacktrace_ops
  * functions. Also handle the case where we need to switch to a new
@@ -144,19 +144,40 @@ void unwind_stack(struct task_struct *task, struct pt_regs *regs,
          * Hopefully this will give us a semi-reliable stacktrace so we
          * can diagnose why curr_unwinder->dump() faulted.
          */
-        if (atomic_inc_return(&unwinder_running) != 1) {
+        if (unwinder_faulted) {
                 spin_lock_irqsave(&unwinder_lock, flags);
 
-                if (!list_is_singular(&unwinder_list)) {
+                /* Make sure no one beat us to changing the unwinder */
+                if (unwinder_faulted && !list_is_singular(&unwinder_list)) {
                         list_del(&curr_unwinder->list);
                         curr_unwinder = select_unwinder();
+
+                        unwinder_faulted = 0;
                 }
 
                 spin_unlock_irqrestore(&unwinder_lock, flags);
-                atomic_dec(&unwinder_running);
         }
 
         curr_unwinder->dump(task, regs, sp, ops, data);
+}
+
+/*
+ * Trap handler for UWINDER_BUG() statements. We must switch to the
+ * unwinder with the next highest rating.
+ */
+BUILD_TRAP_HANDLER(unwinder)
+{
+        insn_size_t insn;
+        TRAP_HANDLER_DECL;
+
+        /* Rewind */
+        regs->pc -= instruction_size(ctrl_inw(regs->pc - 4));
+        insn = *(insn_size_t *)instruction_pointer(regs);
+
+        /* Switch unwinders when unwind_stack() is called */
+        unwinder_faulted = 1;
 
-        atomic_dec(&unwinder_running);
+#ifdef CONFIG_BUG
+        handle_BUG(regs);
+#endif
 }