6.16-stable review patch. If anyone has any objections, please let me know.
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From: Tiezhu Yang yangtiezhu@loongson.cn
commit 677d4a52d4dc4a147d5e84af9ff207832578be70 upstream.
When testing the kernel live patching with "modprobe livepatch-sample", there is a timeout over 15 seconds from "starting patching transition" to "patching complete". The dmesg command 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, in order 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 a 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: stable@vger.kernel.org # v6.9+ Fixes: 199cc14cb4f1 ("LoongArch: Add kernel livepatching support") Reported-by: Xi Zhang zhangxi@kylinos.cn Signed-off-by: Tiezhu Yang yangtiezhu@loongson.cn Signed-off-by: Huacai Chen chenhuacai@loongson.cn Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/loongarch/kernel/stacktrace.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
--- a/arch/loongarch/kernel/stacktrace.c +++ b/arch/loongarch/kernel/stacktrace.c @@ -51,12 +51,13 @@ int arch_stack_walk_reliable(stack_trace 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)) {