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: [email protected] # v6.9+
Fixes: 199cc14cb4f1 ("LoongArch: Add kernel livepatching support")
Reported-by: Xi Zhang <[email protected]>
Signed-off-by: Tiezhu Yang <[email protected]>
---
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
