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Date:   Wed, 8 Nov 2017 10:05:50 -0800
From:   Linus Torvalds <>
To:     Fengguang Wu <>
Cc:     Jeff Kirsher <>,
        Network Development <>,
        "David S. Miller" <>,
        Linux Kernel Mailing List <>,
Subject: Re: [vlan_device_event] BUG: unable to handle kernel paging request
 at 6b6b6ccf

On Wed, Nov 8, 2017 at 9:12 AM, Fengguang Wu <> wrote:
> OK. Here is the original faddr2line output:
> $ ~/linux/scripts/faddr2line vmlinux vlan_device_event+0x7f5/0xa40
> vlan_device_event+0x7f5/0xa40:
> vlan_device_event at net/8021q/vlan.h:60

Hmm. Yes, that's not what I hoped for.

> I notice that this trace shows no additional inline files at all.
> Is it because I did some kconfig option wrong, so that inline info is
> lost? Eg.
> CONFIG_OPTIMIZE_INLINING=y (reading lib/Kconfig.debug, it looks better set  to N)

Hmm. It might also be a compiler/linker issue. Debug info is sadly
often a second class citizen, because it's generally not something
that gets tested nearly as much as the actual _code_ that a compiler

So we've certainly had issues before with incomplete debug info.

That said, I'm not sure how well that CONFIG_DEBUG_INFO_SPLIT works,
I've only ever tested with


which was the config that my scheduler example was generated from.

It might be an issue with the particular version of 'addr2line' too,
for all I know. The one I have is

    GNU addr2line version 2.27-24.fc26

and who knows what else could influence it. I *thought* that as long
as you just had DEBUG_INFO enabled, it would automatically be ok, but
I was clearly wrong.

> [  745.719623] BUG: unable to handle kernel paging request at 6b6b6f4f
> [  745.732871] IP: vlan_device_event+0x7f5/0xa40:
> vlan_device_event at net/8021q/vlan.h:60

Ok, at least now there's no lost information, even if it doesn't have
that nice inlining information that I was hoping for.


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