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powerpc/stacktrace: Fix arch_stack_walk_reliable()

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The changes to copy_thread() made in commit eed7c420aa ("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 edbd0387f3 ("powerpc: copy_thread add a back chain to the
switch stack frame"), so remove that as well.

Fixes: eed7c420aa ("powerpc: copy_thread differentiate kthreads and user mode threads")
Reported-by: Joe Lawrence <joe.lawrence@redhat.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230921232441.1181843-1-mpe@ellerman.id.au
This commit is contained in:
Michael Ellerman 2023-09-22 09:24:41 +10:00
parent c3f4309693
commit c5cc3ca707
1 changed files with 5 additions and 22 deletions
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27
arch/powerpc/kernel/stacktrace.c
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@ -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();