1 files changed, 31 insertions, 5 deletions

diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
index 695538031c69..045d987bc683 100644
--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -399,7 +399,7 @@ unsigned long thread_saved_pc(struct task_struct *tsk)
 #ifdef CONFIG_KALLSYMS
 /* used by show_backtrace() */
 unsigned long unwind_stack(struct task_struct *task, unsigned long *sp,
-                           unsigned long pc, unsigned long ra)
+                           unsigned long pc, unsigned long *ra)
 {
         unsigned long stack_page;
         struct mips_frame_info info;
@@ -407,18 +407,42 @@ unsigned long unwind_stack(struct task_struct *task, unsigned long *sp,
         char namebuf[KSYM_NAME_LEN + 1];
         unsigned long size, ofs;
         int leaf;
+        extern void ret_from_irq(void);
+        extern void ret_from_exception(void);
 
         stack_page = (unsigned long)task_stack_page(task);
         if (!stack_page)
                 return 0;
 
+        /*
+         * If we reached the bottom of interrupt context,
+         * return saved pc in pt_regs.
+         */
+        if (pc == (unsigned long)ret_from_irq ||
+            pc == (unsigned long)ret_from_exception) {
+                struct pt_regs *regs;
+                if (*sp >= stack_page &&
+                    *sp + sizeof(*regs) <= stack_page + THREAD_SIZE - 32) {
+                        regs = (struct pt_regs *)*sp;
+                        pc = regs->cp0_epc;
+                        if (__kernel_text_address(pc)) {
+                                *sp = regs->regs[29];
+                                *ra = regs->regs[31];
+                                return pc;
+                        }
+                }
+                return 0;
+        }
         if (!kallsyms_lookup(pc, &size, &ofs, &modname, namebuf))
                 return 0;
         /*
          * Return ra if an exception occured at the first instruction
          */
-        if (unlikely(ofs == 0))
-                return ra;
+        if (unlikely(ofs == 0)) {
+                pc = *ra;
+                *ra = 0;
+                return pc;
+        }
 
         info.func = (void *)(pc - ofs);
         info.func_size = ofs;   /* analyze from start to ofs */
@@ -437,11 +461,12 @@ unsigned long unwind_stack(struct task_struct *task, unsigned long *sp,
                  * one. In that cases avoid to return always the
                  * same value.
                  */
-                pc = pc != ra ? ra : 0;
+                pc = pc != *ra ? *ra : 0;
         else
                 pc = ((unsigned long *)(*sp))[info.pc_offset];
 
         *sp += info.frame_size;
+        *ra = 0;
         return __kernel_text_address(pc) ? pc : 0;
 }
 #endif
@@ -454,6 +479,7 @@ unsigned long get_wchan(struct task_struct *task)
         unsigned long pc = 0;
 #ifdef CONFIG_KALLSYMS
         unsigned long sp;
+        unsigned long ra = 0;
 #endif
 
         if (!task || task == current || task->state == TASK_RUNNING)
@@ -467,7 +493,7 @@ unsigned long get_wchan(struct task_struct *task)
         sp = task->thread.reg29 + schedule_mfi.frame_size;
 
         while (in_sched_functions(pc))
-                pc = unwind_stack(task, &sp, pc, 0);
+                pc = unwind_stack(task, &sp, pc, &ra);
 #endif
 
 out: