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m68k: Fix backtraces for non-running tasks

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When no stack pointer is supplied, show_stack() starts at thread.esp0.
This is the saved userspace register frame, not where a task was switched
out. For kernel threads it points to the zeroed frame created by
copy_thread(), so sched_show_task() prints no useful backtrace.

Use thread.ksp for non-current tasks. It is saved by switch_to() and is
already used by __get_wchan(). For current, start at the current stack
frame, as is already done when no task is supplied.

Tested on qemu-system-m68k -M virt using SysRq-t. All task dumps contained
resolved frames.

Fixes: 1da177e4c3 ("Linux-2.6.12-rc2")
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Karl Mehltretter <kmehltretter@gmail.com>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Tested-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: https://patch.msgid.link/20260723041055.47289-1-kmehltretter@gmail.com
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
This commit is contained in:
Karl Mehltretter 2026-07-23 06:10:55 +02:00 committed by Geert Uytterhoeven
parent 993e1b93db
commit 09f71dbeb2
1 changed files with 2 additions and 2 deletions
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4
arch/m68k/kernel/traps.c
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@ -936,8 +936,8 @@ void show_stack(struct task_struct *task, unsigned long *stack,
int i;
if (!stack) {
if (task)
stack = (unsigned long *)task->thread.esp0;
if (task && task != current)
stack = (unsigned long *)task->thread.ksp;
else
stack = (unsigned long *)&stack;
}