Re: Recent Power changes and stack_trace_save_tsk_reliable?

[Michael Ellerman <mpe@ellerman.id.au>]

Michael Ellerman <mpe@ellerman.id.au> writes:
> Joe Lawrence <joe.lawrence@redhat.com> writes:
>> Hi ppc-dev list,
>>
>> We noticed that our kpatch integration tests started failing on ppc64le
>> when targeting the upstream v6.4 kernel, and then confirmed that the
>> in-tree livepatching kselftests similarly fail, too.  From the kselftest
>> results, it appears that livepatch transitions are no longer completing.
>
> Hi Joe,
>
> Thanks for the report.
>
> I thought I was running the livepatch tests, but looks like somewhere
> along the line my kernel .config lost CONFIG_TEST_LIVEPATCH=m, so I have
> been running the test but it just skips. :/
>
> I can reproduce the failure, and will see if I can bisect it more
> successfully.

It's caused by:

  eed7c420aac7 ("powerpc: copy_thread differentiate kthreads and user mode threads")

Which is obvious in hindsight :)

The diff below fixes it for me, can you test that on your setup?

A proper fix will need to be a bit bigger because the comments in there
are all slightly wrong now since the above commit.

Possibly we can also rework that code more substantially now that
copy_thread() is more careful about setting things up, but that would be
a follow-up.

diff --git a/arch/powerpc/kernel/stacktrace.c b/arch/powerpc/kernel/stacktrace.c
index 5de8597eaab8..d0b3509f13ee 100644
--- a/arch/powerpc/kernel/stacktrace.c
+++ b/arch/powerpc/kernel/stacktrace.c
@@ -73,7 +73,7 @@ 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)) {
+	if (!(task->flags & PF_KTHREAD)) {
 		/*
 		 * For user tasks, this is the SP value loaded on
 		 * kernel entry, see "PACAKSAVE(r13)" in _switch() and


cheers