On 2025-09-09 19:31, Tiezhu Yang 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. When executing "rmmod livepatch-sample", there exists the similar issue.Like x86, arch_stack_walk_reliable() should return 0 for user tasks. It is necessary to set regs->csr_prmd as task->thread.csr_prmd first, then use user_mode() to check whether the task is in userspace. 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() 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 [Sat Sep 6 11:19:00 2025] livepatch: 'livepatch_sample': starting patching transition [Sat Sep 6 11:19:01 2025] livepatch: 'livepatch_sample': patching complete # echo 0 > /sys/kernel/livepatch/livepatch_sample/enabled # rmmod livepatch_sample # dmesg -T | tail -2 [Sat Sep 6 11:21:10 2025] livepatch: 'livepatch_sample': starting unpatching transition [Sat Sep 6 11:21:11 2025] livepatch: 'livepatch_sample': unpatching complete While at it, do the similar thing for arch_stack_walk() to avoid potential issues. 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 | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/arch/loongarch/kernel/stacktrace.c b/arch/loongarch/kernel/stacktrace.c index 9a038d1070d7..0454cce3b667 100644 --- a/arch/loongarch/kernel/stacktrace.c +++ b/arch/loongarch/kernel/stacktrace.c @@ -30,10 +30,15 @@ void arch_stack_walk(stack_trace_consume_fn consume_entry, void *cookie, } regs->regs[1] = 0; regs->regs[22] = 0; + regs->csr_prmd = task->thread.csr_prmd; }for (unwind_start(&state, task, regs);!unwind_done(&state); unwind_next_frame(&state)) { + /* Success path for user tasks */ + if (user_mode(regs)) + return; + addr = unwind_get_return_address(&state); if (!addr || !consume_entry(cookie, addr)) break; @@ -57,9 +62,14 @@ int arch_stack_walk_reliable(stack_trace_consume_fn consume_entry, } regs->regs[1] = 0; regs->regs[22] = 0; + regs->csr_prmd = task->thread.csr_prmd;for (unwind_start(&state, task, regs);!unwind_done(&state) && !unwind_error(&state); unwind_next_frame(&state)) { + /* Success path for user tasks */ + if (user_mode(regs)) + return 0; + addr = unwind_get_return_address(&state);/*
Hi, Tiezhu, We update stack info by get_stack_info when meet ORC_TYPE_REGS in unwind_next_frame. And in arch_stack_walk(_reliable), we always do unwind_done before unwind_next_frame. So is there anything error in get_stack_info which causing regs is user_mode while stack is not STACK_TYPE_UNKNOWN?
