The changes to copy_thread() made in commit eed7c420aac7 ("powerpc:
copy_thread differentiate kthreads and user mode threads") inadvertently
broke arch_stack_walk_reliable() because it has knowledge of the stack
layout.
Fix it by changing the condition to match the new logic in
copy_thread(). The changes make the comments about the stack layout
incorrect, rather than rephrasing them just refer the reader to
copy_thread().
Also the comment about the stack backchain is no longer true, since
commit edbd0387f324 ("powerpc: copy_thread add a back chain to the
switch stack frame"), so remove that as well.
Reported-by: Joe Lawrence <joe.lawrence@xxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Fixes: eed7c420aac7 ("powerpc: copy_thread differentiate kthreads and user mode threads")
---
arch/powerpc/kernel/stacktrace.c | 27 +++++----------------------
1 file changed, 5 insertions(+), 22 deletions(-)
diff --git a/arch/powerpc/kernel/stacktrace.c b/arch/powerpc/kernel/stacktrace.c
index b15f15dcacb5..e6a958a5da27 100644
--- a/arch/powerpc/kernel/stacktrace.c
+++ b/arch/powerpc/kernel/stacktrace.c
@@ -73,29 +73,12 @@ int __no_sanitize_address arch_stack_walk_reliable(stack_trace_consume_fn consum
bool firstframe;
stack_end = stack_page + THREAD_SIZE;
- if (!is_idle_task(task)) {
- /*
- * For user tasks, this is the SP value loaded on
- * kernel entry, see "PACAKSAVE(r13)" in _switch() and
- * system_call_common().
- *
- * Likewise for non-swapper kernel threads,
- * this also happens to be the top of the stack
- * as setup by copy_thread().
- *
- * Note that stack backlinks are not properly setup by
- * copy_thread() and thus, a forked task() will have
- * an unreliable stack trace until it's been
- * _switch()'ed to for the first time.
- */
- stack_end -= STACK_USER_INT_FRAME_SIZE;
- } else {
- /*
- * idle tasks have a custom stack layout,
- * c.f. cpu_idle_thread_init().
- */
+
+ // See copy_thread() for details.
+ if (task->flags & PF_KTHREAD)
stack_end -= STACK_FRAME_MIN_SIZE;
- }
+ else
+ stack_end -= STACK_USER_INT_FRAME_SIZE;
if (task == current)
sp = current_stack_frame();
--
2.41.0
