[PATCH 2/2] x86/unwind: Dump all stacks in unwind_dump()

[Josh Poimboeuf]

Currently unwind_dump() dumps only the most recently accessed stack.
But it has a few issues.

In some cases, 'first_sp' can get out of sync with 'stack_info', causing
unwind_dump() to start from the wrong address, flood the printk buffer,
and eventually read a bad address.

In other cases, dumping only the most recently accessed stack doesn't
give enough data to diagnose the error.

Fix both issues by dumping *all* stacks involved in the trace, not just
the last one.

Fixes: 8b5e99f02264 ("x86/unwind: Dump stack data on warnings")
Signed-off-by: Josh Poimboeuf <jpoim...@redhat.com>
---
 arch/x86/kernel/unwind_frame.c | 34 +++++++++++++++++++++-------------
 1 file changed, 21 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kernel/unwind_frame.c b/arch/x86/kernel/unwind_frame.c
index ae0821f..fec70fe 100644
--- a/arch/x86/kernel/unwind_frame.c
+++ b/arch/x86/kernel/unwind_frame.c
@@ -30,6 +30,8 @@ static void unwind_dump(struct unwind_state *state)
        static bool dumped_before = false;
        bool prev_zero, zero = false;
        unsigned long word, *sp;
+       struct stack_info stack_info = {0};
+       unsigned long visit_mask = 0;
 
        if (dumped_before)
                return;
@@ -40,21 +42,27 @@ static void unwind_dump(struct unwind_state *state)
                        state->stack_info.type, state->stack_info.next_sp,
                        state->stack_mask, state->graph_idx);
 
-       for (sp = state->orig_sp; sp < state->stack_info.end; sp++) {
-               word = READ_ONCE_NOCHECK(*sp);
+       for (sp = state->orig_sp; sp; sp = PTR_ALIGN(stack_info.next_sp, 
sizeof(long))) {
+               if (get_stack_info(sp, state->task, &stack_info, &visit_mask))
+                       break;
 
-               prev_zero = zero;
-               zero = word == 0;
+               for (; sp < stack_info.end; sp++) {
 
-               if (zero) {
-                       if (!prev_zero)
-                               printk_deferred("%p: %0*x ...\n",
-                                               sp, BITS_PER_LONG/4, 0);
-                       continue;
-               }
+                       word = READ_ONCE_NOCHECK(*sp);
+
+                       prev_zero = zero;
+                       zero = word == 0;
 
-               printk_deferred("%p: %0*lx (%pB)\n",
-                               sp, BITS_PER_LONG/4, word, (void *)word);
+                       if (zero) {
+                               if (!prev_zero)
+                                       printk_deferred("%p: %0*x ...\n",
+                                                       sp, BITS_PER_LONG/4, 0);
+                               continue;
+                       }
+
+                       printk_deferred("%p: %0*lx (%pB)\n",
+                                       sp, BITS_PER_LONG/4, word, (void 
*)word);
+               }
        }
 }
 
@@ -216,7 +224,7 @@ static bool update_stack_state(struct unwind_state *state,
        }
 
        /* Save the original stack pointer for unwind_dump(): */
-       if (!state->orig_sp || info->type != prev_type)
+       if (!state->orig_sp)
                state->orig_sp = frame;
 
        return true;
-- 
2.7.4