Re: Question: livepatch failed for new fork() task stack unreliable

[Josh Poimboeuf <jpoimboe@redhat.com>]

On Tue, Jun 02, 2020 at 09:22:30AM +0800, Wangshaobo (bobo) wrote:
> so i think this question is related to ORC unwinder, could i ask if you have
> strategy or plan to avoid this problem ?

I suspect something like this would fix it (untested):

diff --git a/arch/x86/kernel/stacktrace.c b/arch/x86/kernel/stacktrace.c
index 6ad43fc44556..8cf95ded1410 100644
--- a/arch/x86/kernel/stacktrace.c
+++ b/arch/x86/kernel/stacktrace.c
@@ -50,7 +50,7 @@ int arch_stack_walk_reliable(stack_trace_consume_fn consume_entry,
 		if (regs) {
 			/* Success path for user tasks */
 			if (user_mode(regs))
-				return 0;
+				break;
 
 			/*
 			 * Kernel mode registers on the stack indicate an
@@ -81,10 +81,6 @@ int arch_stack_walk_reliable(stack_trace_consume_fn consume_entry,
 	if (unwind_error(&state))
 		return -EINVAL;
 
-	/* Success path for non-user tasks, i.e. kthreads and idle tasks */
-	if (!(task->flags & (PF_KTHREAD | PF_IDLE)))
-		return -EINVAL;
-
 	return 0;
 }
 
diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
index 7f969b2d240f..d7396431261a 100644
--- a/arch/x86/kernel/unwind_orc.c
+++ b/arch/x86/kernel/unwind_orc.c
@@ -540,7 +540,7 @@ bool unwind_next_frame(struct unwind_state *state)
 		state->sp = sp;
 		state->regs = NULL;
 		state->prev_regs = NULL;
-		state->signal = false;
+		state->signal = ((void *)state->ip == ret_from_fork);
 		break;
 
 	case ORC_TYPE_REGS: