Commit c5cc3ca7 authored by Michael Ellerman's avatar Michael Ellerman
Browse files

powerpc/stacktrace: Fix arch_stack_walk_reliable() 



The changes to copy_thread() made in commit eed7c420 ("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 edbd0387 ("powerpc: copy_thread add a back chain to the
switch stack frame"), so remove that as well.

Fixes: eed7c420 ("powerpc: copy_thread differentiate kthreads and user mode threads")
Reported-by: default avatarJoe Lawrence <joe.lawrence@redhat.com>
Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230921232441.1181843-1-mpe@ellerman.id.au
parent c3f43096

arch/powerpc/kernel/stacktrace.c

+5 −22
Original line number Diff line number Diff line
@@ -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();