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

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Message-ID: <20200602131450.oydrydelpdaval4h@treble>
Date:   Tue, 2 Jun 2020 08:14:50 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     "Wangshaobo (bobo)" <bobo.shaobowang@...wei.com>
Cc:     huawei.libin@...wei.com, xiexiuqi@...wei.com,
        cj.chengjian@...wei.com, mingo@...hat.com, x86@...nel.org,
        linux-kernel@...r.kernel.org, live-patching@...r.kernel.org,
        mbenes@...e.cz, devel@...ukata.com, viro@...iv.linux.org.uk,
        esyr@...hat.com
Subject: Re: Question: livepatch failed for new fork() task stack unreliable

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: