powerpc/livepatch: small cleanups in save_stack_trace_tsk_reliable()

Mostly cosmetic changes:

- Group common stack pointer code at the top
- Simplify the first frame logic
- Code stackframe iteration into for...loop construct
- Check for trace->nr_entries overflow before adding any into the array

Suggested-by: Nicolai Stange <nstange@suse.de>
Signed-off-by: Joe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

1 files changed, 14 insertions, 26 deletions

diff --git a/arch/powerpc/kernel/stacktrace.c b/arch/powerpc/kernel/stacktrace.c
index 06688f4d557b..28c3c25755d7 100644
--- a/arch/powerpc/kernel/stacktrace.c
+++ b/arch/powerpc/kernel/stacktrace.c
@@ -95,20 +95,11 @@ save_stack_trace_tsk_reliable(struct task_struct *tsk,
                                 struct stack_trace *trace)
 {
         unsigned long sp;
+        unsigned long newsp;
         unsigned long stack_page = (unsigned long)task_stack_page(tsk);
         unsigned long stack_end;
         int graph_idx = 0;
-
-        /*
-         * The last frame (unwinding first) may not yet have saved
-         * its LR onto the stack.
-         */
-        int firstframe = 1;
-
-        if (tsk == current)
-                sp = current_stack_pointer();
-        else
-                sp = tsk->thread.ksp;
+        bool firstframe;
 
         stack_end = stack_page + THREAD_SIZE;
         if (!is_idle_task(tsk)) {
@@ -135,14 +126,20 @@ save_stack_trace_tsk_reliable(struct task_struct *tsk,
                 stack_end -= STACK_FRAME_OVERHEAD;
         }
 
+        if (tsk == current)
+                sp = current_stack_pointer();
+        else
+                sp = tsk->thread.ksp;
+
         if (sp < stack_page + sizeof(struct thread_struct) ||
             sp > stack_end - STACK_FRAME_MIN_SIZE) {
                 return 1;
         }
 
-        for (;;) {
+        for (firstframe = true; sp != stack_end;
+             firstframe = false, sp = newsp) {
                 unsigned long *stack = (unsigned long *) sp;
-                unsigned long newsp, ip;
+                unsigned long ip;
 
                 /* sanity check: ABI requires SP to be aligned 16 bytes. */
                 if (sp & 0xF)
@@ -163,10 +160,8 @@ save_stack_trace_tsk_reliable(struct task_struct *tsk,
                  * rest of the frame may be uninitialized, continue to
                  * the next.
                  */
-                if (firstframe) {
-                        firstframe = 0;
-                        goto next;
-                }
+                if (firstframe)
+                        continue;
 
                 /* Mark stacktraces with exception frames as unreliable. */
                 if (sp <= stack_end - STACK_INT_FRAME_SIZE &&
@@ -193,19 +188,12 @@ save_stack_trace_tsk_reliable(struct task_struct *tsk,
                         return 1;
 #endif
 
+                if (trace->nr_entries >= trace->max_entries)
+                        return -E2BIG;
                 if (!trace->skip)
                         trace->entries[trace->nr_entries++] = ip;
                 else
                         trace->skip--;
-
-next:
-                if (newsp == stack_end)
-                        break;
-
-                if (trace->nr_entries >= trace->max_entries)
-                        return -E2BIG;
-
-                sp = newsp;
         }
         return 0;
 }