linux-kernel - Re: [2/2] x86/unwind: Make CONFIG_UNWINDER_ORC=y the default in kconfig for 64-bit

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Date:   Thu, 19 Oct 2017 13:16:55 -0500
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Andrei Vagin <avagin@...tuozzo.com>
Cc:     Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
        torvalds@...ux-foundation.org, peterz@...radead.org, hpa@...or.com,
        tglx@...utronix.de
Subject: Re: [2/2] x86/unwind: Make CONFIG_UNWINDER_ORC=y the default in
 kconfig for 64-bit

On Thu, Oct 19, 2017 at 09:51:04AM -0700, Andrei Vagin wrote:
> Hi,
> 
> We run CRIU tests for tip/auto-latest regularly, and a few days ago our
> test job started to detect this warning in a kernel log:
> 
> [   44.235786] WARNING: can't dereference iret registers at ffff8801c5f17fe0 for ip ffffffff95f0d94b
> 
> What does it mean? How critical is it?
> 
> Our test job fails if it detects any warning in a kernel log. Maybe we
> need to investigate reasons of this warning and try to eliminate it?
> 
> Here are logs:
> https://travis-ci.org/avagin/linux/jobs/289676634

I think it means the unwinder found some bad ORC unwinder metadata.  Any
chance you have access to the kernel binary?  I need to know what code
corresponds to that ffffffff95f0d94b address.

Or if you can reproduce with the following patch, that should help:


diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c
index 570b70d3f604..95b633f0ce51 100644
--- a/arch/x86/kernel/unwind_orc.c
+++ b/arch/x86/kernel/unwind_orc.c
@@ -448,7 +448,7 @@ bool unwind_next_frame(struct unwind_state *state)
 
 	case ORC_TYPE_REGS_IRET:
 		if (!deref_stack_regs(state, sp, &state->ip, &state->sp, false)) {
-			orc_warn("can't dereference iret registers at %p for ip %p\n",
+			orc_warn("can't dereference iret registers at %p for ip %pB\n",
 				 (void *)sp, (void *)orig_ip);
 			goto done;
 		}