[MIPS] Make unwind_stack() can dig into interrupted context

If the PC was ret_from_irq or ret_from_exception, there will be no
more normal stackframe.  Instead of stopping the unwinding, use PC and
RA saved by an exception handler to continue unwinding into the
interrupted context.  This also simplifies the CONFIG_STACKTRACE code.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

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: