Applied, thanks.
Huacai
On Tue, Sep 16, 2025 at 5:35 PM Tiezhu Yang <yangtie...@loongson.cn> wrote:
>
> When testing the kernel live patching with "modprobe livepatch-sample",
> there is a timeout over 15 seconds from "starting patching transition"
> to "patching complete", dmesg shows "unreliable stack" for user tasks
> in debug mode, here is one of the messages:
>
> livepatch: klp_try_switch_task: bash:1193 has an unreliable stack
>
> The "unreliable stack" is because it can not unwind from do_syscall()
> to its previous frame handle_syscall(), it should use fp to find the
> original stack top due to secondary stack in do_syscall(), but fp is
> not used for some other functions, then fp can not be restored by the
> next frame of do_syscall(), so it is necessary to save fp if task is
> not current to get the stack top of do_syscall().
>
> Here are the call chains:
>
> klp_enable_patch()
> klp_try_complete_transition()
> klp_try_switch_task()
> klp_check_and_switch_task()
> klp_check_stack()
> stack_trace_save_tsk_reliable()
> arch_stack_walk_reliable()
>
> When executing "rmmod livepatch-sample", there exists the similar issue.
> With this patch, it takes a short time for patching and unpatching.
>
> Before:
>
> # modprobe livepatch-sample
> # dmesg -T | tail -3
> [Sat Sep 6 11:00:20 2025] livepatch: 'livepatch_sample': starting patching
> transition
> [Sat Sep 6 11:00:35 2025] livepatch: signaling remaining tasks
> [Sat Sep 6 11:00:36 2025] livepatch: 'livepatch_sample': patching complete
>
> # echo 0 > /sys/kernel/livepatch/livepatch_sample/enabled
> # rmmod livepatch_sample
> rmmod: ERROR: Module livepatch_sample is in use
> # rmmod livepatch_sample
> # dmesg -T | tail -3
> [Sat Sep 6 11:06:05 2025] livepatch: 'livepatch_sample': starting
> unpatching transition
> [Sat Sep 6 11:06:20 2025] livepatch: signaling remaining tasks
> [Sat Sep 6 11:06:21 2025] livepatch: 'livepatch_sample': unpatching
> complete
>
> After:
>
> # modprobe livepatch-sample
> # dmesg -T | tail -2
> [Tue Sep 16 16:19:30 2025] livepatch: 'livepatch_sample': starting patching
> transition
> [Tue Sep 16 16:19:31 2025] livepatch: 'livepatch_sample': patching complete
>
> # echo 0 > /sys/kernel/livepatch/livepatch_sample/enabled
> # rmmod livepatch_sample
> # dmesg -T | tail -2
> [Tue Sep 16 16:19:36 2025] livepatch: 'livepatch_sample': starting
> unpatching transition
> [Tue Sep 16 16:19:37 2025] livepatch: 'livepatch_sample': unpatching
> complete
>
> Cc: sta...@vger.kernel.org # v6.9+
> Fixes: 199cc14cb4f1 ("LoongArch: Add kernel livepatching support")
> Reported-by: Xi Zhang <zhan...@kylinos.cn>
> Signed-off-by: Tiezhu Yang <yangtie...@loongson.cn>
> ---
> arch/loongarch/kernel/stacktrace.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/arch/loongarch/kernel/stacktrace.c
> b/arch/loongarch/kernel/stacktrace.c
> index 9a038d1070d7..387dc4d3c486 100644
> --- a/arch/loongarch/kernel/stacktrace.c
> +++ b/arch/loongarch/kernel/stacktrace.c
> @@ -51,12 +51,13 @@ int arch_stack_walk_reliable(stack_trace_consume_fn
> consume_entry,
> if (task == current) {
> regs->regs[3] = (unsigned long)__builtin_frame_address(0);
> regs->csr_era = (unsigned long)__builtin_return_address(0);
> + regs->regs[22] = 0;
> } else {
> regs->regs[3] = thread_saved_fp(task);
> regs->csr_era = thread_saved_ra(task);
> + regs->regs[22] = task->thread.reg22;
> }
> regs->regs[1] = 0;
> - regs->regs[22] = 0;
>
> for (unwind_start(&state, task, regs);
> !unwind_done(&state) && !unwind_error(&state);
> unwind_next_frame(&state)) {
> --
> 2.42.0
>
