4 files changed, 60 insertions, 20 deletions

diff --git a/arch/mips/include/asm/irq.h b/arch/mips/include/asm/irq.h
index 956db6e201d1..ddd1c918103b 100644
--- a/arch/mips/include/asm/irq.h
+++ b/arch/mips/include/asm/irq.h
@@ -18,9 +18,24 @@
 #include <irq.h>
 
 #define IRQ_STACK_SIZE                  THREAD_SIZE
+#define IRQ_STACK_START                 (IRQ_STACK_SIZE - sizeof(unsigned long))
 
 extern void *irq_stack[NR_CPUS];
 
+/*
+ * The highest address on the IRQ stack contains a dummy frame put down in
+ * genex.S (handle_int & except_vec_vi_handler) which is structured as follows:
+ *
+ *   top ------------
+ *       | task sp  | <- irq_stack[cpu] + IRQ_STACK_START
+ *       ------------
+ *       |          | <- First frame of IRQ context
+ *       ------------
+ *
+ * task sp holds a copy of the task stack pointer where the struct pt_regs
+ * from exception entry can be found.
+ */
+
 static inline bool on_irq_stack(int cpu, unsigned long sp)
 {
         unsigned long low = (unsigned long)irq_stack[cpu];
diff --git a/arch/mips/kernel/asm-offsets.c b/arch/mips/kernel/asm-offsets.c
index bb5c5d34ba81..a670c0c11875 100644
--- a/arch/mips/kernel/asm-offsets.c
+++ b/arch/mips/kernel/asm-offsets.c
@@ -102,6 +102,7 @@ void output_thread_info_defines(void)
         DEFINE(_THREAD_SIZE, THREAD_SIZE);
         DEFINE(_THREAD_MASK, THREAD_MASK);
         DEFINE(_IRQ_STACK_SIZE, IRQ_STACK_SIZE);
+        DEFINE(_IRQ_STACK_START, IRQ_STACK_START);
         BLANK();
 }
 
diff --git a/arch/mips/kernel/genex.S b/arch/mips/kernel/genex.S
index 2ac6c2625c13..ae810da4d499 100644
--- a/arch/mips/kernel/genex.S
+++ b/arch/mips/kernel/genex.S
@@ -215,9 +215,11 @@ NESTED(handle_int, PT_SIZE, sp)
         beq     t0, t1, 2f
 
         /* Switch to IRQ stack */
-        li      t1, _IRQ_STACK_SIZE
+        li      t1, _IRQ_STACK_START
         PTR_ADD sp, t0, t1
 
+        /* Save task's sp on IRQ stack so that unwinding can follow it */
+        LONG_S  s1, 0(sp)
 2:
         jal     plat_irq_dispatch
 
@@ -325,9 +327,11 @@ NESTED(except_vec_vi_handler, 0, sp)
         beq     t0, t1, 2f
 
         /* Switch to IRQ stack */
-        li      t1, _IRQ_STACK_SIZE
+        li      t1, _IRQ_STACK_START
         PTR_ADD sp, t0, t1
 
+        /* Save task's sp on IRQ stack so that unwinding can follow it */
+        LONG_S  s1, 0(sp)
 2:
         jalr    v0
 
diff --git a/arch/mips/kernel/process.c b/arch/mips/kernel/process.c
index fb6b6b650719..b68e10fc453d 100644
--- a/arch/mips/kernel/process.c
+++ b/arch/mips/kernel/process.c
@@ -488,31 +488,52 @@ unsigned long notrace unwind_stack_by_address(unsigned long stack_page,
                                               unsigned long pc,
                                               unsigned long *ra)
 {
+        unsigned long low, high, irq_stack_high;
         struct mips_frame_info info;
         unsigned long size, ofs;
+        struct pt_regs *regs;
         int leaf;
-        extern void ret_from_irq(void);
-        extern void ret_from_exception(void);
 
         if (!stack_page)
                 return 0;
 
         /*
-         * If we reached the bottom of interrupt context,
-         * return saved pc in pt_regs.
+         * IRQ stacks start at IRQ_STACK_START
+         * task stacks at THREAD_SIZE - 32
          */
-        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 (!user_mode(regs) && __kernel_text_address(pc)) {
-                                *sp = regs->regs[29];
-                                *ra = regs->regs[31];
-                                return pc;
-                        }
+        low = stack_page;
+        if (!preemptible() && on_irq_stack(raw_smp_processor_id(), *sp)) {
+                high = stack_page + IRQ_STACK_START;
+                irq_stack_high = high;
+        } else {
+                high = stack_page + THREAD_SIZE - 32;
+                irq_stack_high = 0;
+        }
+
+        /*
+         * If we reached the top of the interrupt stack, start unwinding
+         * the interrupted task stack.
+         */
+        if (unlikely(*sp == irq_stack_high)) {
+                unsigned long task_sp = *(unsigned long *)*sp;
+
+                /*
+                 * Check that the pointer saved in the IRQ stack head points to
+                 * something within the stack of the current task
+                 */
+                if (!object_is_on_stack((void *)task_sp))
+                        return 0;
+
+                /*
+                 * Follow pointer to tasks kernel stack frame where interrupted
+                 * state was saved.
+                 */
+                regs = (struct pt_regs *)task_sp;
+                pc = regs->cp0_epc;
+                if (!user_mode(regs) && __kernel_text_address(pc)) {
+                        *sp = regs->regs[29];
+                        *ra = regs->regs[31];
+                        return pc;
                 }
                 return 0;
         }
@@ -533,8 +554,7 @@ unsigned long notrace unwind_stack_by_address(unsigned long stack_page,
         if (leaf < 0)
                 return 0;
 
-        if (*sp < stack_page ||
-            *sp + info.frame_size > stack_page + THREAD_SIZE - 32)
+        if (*sp < low || *sp + info.frame_size > high)
                 return 0;
 
         if (leaf)