1 files changed, 22 insertions, 13 deletions

diff --git a/arch/tile/kernel/stack.c b/arch/tile/kernel/stack.c
index ea2e0ce28380..0d54106be3d6 100644
--- a/arch/tile/kernel/stack.c
+++ b/arch/tile/kernel/stack.c
@@ -30,6 +30,10 @@
 #include <arch/abi.h>
 #include <arch/interrupts.h>
 
+#define KBT_ONGOING     0  /* Backtrace still ongoing */
+#define KBT_DONE        1  /* Backtrace cleanly completed */
+#define KBT_RUNNING     2  /* Can't run backtrace on a running task */
+#define KBT_LOOP        3  /* Backtrace entered a loop */
 
 /* Is address on the specified kernel stack? */
 static int in_kernel_stack(struct KBacktraceIterator *kbt, VirtualAddress sp)
@@ -207,11 +211,11 @@ static int KBacktraceIterator_next_item_inclusive(
         for (;;) {
                 do {
                         if (!KBacktraceIterator_is_sigreturn(kbt))
-                                return 1;
+                                return KBT_ONGOING;
                 } while (backtrace_next(&kbt->it));
 
                 if (!KBacktraceIterator_restart(kbt))
-                        return 0;
+                        return KBT_DONE;
         }
 }
 
@@ -264,7 +268,7 @@ void KBacktraceIterator_init(struct KBacktraceIterator *kbt,
         kbt->pgtable = NULL;
         kbt->verbose = 0;   /* override in caller if desired */
         kbt->profile = 0;   /* override in caller if desired */
-        kbt->end = 0;
+        kbt->end = KBT_ONGOING;
         kbt->new_context = 0;
         if (is_current) {
                 HV_PhysAddr pgdir_pa = hv_inquire_context().page_table;
@@ -290,7 +294,7 @@ void KBacktraceIterator_init(struct KBacktraceIterator *kbt,
         if (regs == NULL) {
                 if (is_current || t->state == TASK_RUNNING) {
                         /* Can't do this; we need registers */
-                        kbt->end = 1;
+                        kbt->end = KBT_RUNNING;
                         return;
                 }
                 pc = get_switch_to_pc();
@@ -305,26 +309,29 @@ void KBacktraceIterator_init(struct KBacktraceIterator *kbt,
         }
 
         backtrace_init(&kbt->it, read_memory_func, kbt, pc, lr, sp, r52);
-        kbt->end = !KBacktraceIterator_next_item_inclusive(kbt);
+        kbt->end = KBacktraceIterator_next_item_inclusive(kbt);
 }
 EXPORT_SYMBOL(KBacktraceIterator_init);
 
 int KBacktraceIterator_end(struct KBacktraceIterator *kbt)
 {
-        return kbt->end;
+        return kbt->end != KBT_ONGOING;
 }
 EXPORT_SYMBOL(KBacktraceIterator_end);
 
 void KBacktraceIterator_next(struct KBacktraceIterator *kbt)
 {
+        VirtualAddress old_pc = kbt->it.pc, old_sp = kbt->it.sp;
         kbt->new_context = 0;
-        if (!backtrace_next(&kbt->it) &&
-            !KBacktraceIterator_restart(kbt)) {
-                        kbt->end = 1;
-                        return;
-                }
-
-        kbt->end = !KBacktraceIterator_next_item_inclusive(kbt);
+        if (!backtrace_next(&kbt->it) && !KBacktraceIterator_restart(kbt)) {
+                kbt->end = KBT_DONE;
+                return;
+        }
+        kbt->end = KBacktraceIterator_next_item_inclusive(kbt);
+        if (old_pc == kbt->it.pc && old_sp == kbt->it.sp) {
+                /* Trapped in a loop; give up. */
+                kbt->end = KBT_LOOP;
+        }
 }
 EXPORT_SYMBOL(KBacktraceIterator_next);
 
@@ -387,6 +394,8 @@ void tile_show_stack(struct KBacktraceIterator *kbt, int headers)
                         break;
                 }
         }
+        if (kbt->end == KBT_LOOP)
+                pr_err("Stack dump stopped; next frame identical to this one\n");
         if (headers)
                 pr_err("Stack dump complete\n");
 }