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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Fengguang Wu <fengguang.wu@intel.com>
Cc: Jeff Kirsher <jeffrey.t.kirsher@intel.com>,
	Network Development <netdev@vger.kernel.org>,
	"David S. Miller" <davem@davemloft.net>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	intel-wired-lan@lists.osuosl.org
Subject: Re: [vlan_device_event] BUG: unable to handle kernel paging request at 6b6b6ccf
Date: Wed, 8 Nov 2017 10:05:50 -0800	[thread overview]
Message-ID: <CA+55aFxohPiat5DpPqfxiJqvChKqq=giL-FMPbbVPkdcP49SEA@mail.gmail.com> (raw)
In-Reply-To: <20171108171230.ccf7lwutjysk26fc@wfg-t540p.sh.intel.com>

On Wed, Nov 8, 2017 at 9:12 AM, Fengguang Wu <fengguang.wu@intel.com> 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)
> CONFIG_DEBUG_INFO_REDUCED=y
> CONFIG_DEBUG_INFO_SPLIT=y

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
generates.

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

  CONFIG_DEBUG_INFO=y
  CONFIG_DEBUG_INFO_REDUCED=y
  # CONFIG_DEBUG_INFO_SPLIT is not set
  # CONFIG_DEBUG_INFO_DWARF4 is not set

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.

              Linus

WARNING: multiple messages have this Message-ID
From: Linus Torvalds <torvalds@linux-foundation.org>
To: intel-wired-lan@osuosl.org
Subject: [Intel-wired-lan] [vlan_device_event] BUG: unable to handle kernel paging request at 6b6b6ccf
Date: Wed, 8 Nov 2017 10:05:50 -0800	[thread overview]
Message-ID: <CA+55aFxohPiat5DpPqfxiJqvChKqq=giL-FMPbbVPkdcP49SEA@mail.gmail.com> (raw)
In-Reply-To: <20171108171230.ccf7lwutjysk26fc@wfg-t540p.sh.intel.com>

On Wed, Nov 8, 2017 at 9:12 AM, Fengguang Wu <fengguang.wu@intel.com> 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)
> CONFIG_DEBUG_INFO_REDUCED=y
> CONFIG_DEBUG_INFO_SPLIT=y

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
generates.

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

  CONFIG_DEBUG_INFO=y
  CONFIG_DEBUG_INFO_REDUCED=y
  # CONFIG_DEBUG_INFO_SPLIT is not set
  # CONFIG_DEBUG_INFO_DWARF4 is not set

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.

              Linus

  parent reply	other threads:[~2017-11-08 18:05 UTC|newest]

Thread overview: 58+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-07 10:21 [vlan_device_event] BUG: unable to handle kernel paging request at 6b6b6ccf Fengguang Wu
2017-11-07 16:25 ` Linus Torvalds
2017-11-07 16:46   ` Fengguang Wu
2017-11-08  9:48   ` Fengguang Wu
2017-11-08 16:20     ` Linus Torvalds
2017-11-08 16:20       ` [Intel-wired-lan] " Linus Torvalds
2017-11-08 17:12       ` Fengguang Wu
2017-11-08 17:12         ` [Intel-wired-lan] " Fengguang Wu
2017-11-08 17:18         ` Fengguang Wu
2017-11-08 17:18           ` [Intel-wired-lan] " Fengguang Wu
2017-11-08 18:05         ` Linus Torvalds [this message]
2017-11-08 18:05           ` Linus Torvalds
2017-11-08 18:36         ` Alexander Duyck
2017-11-08 18:36           ` [Intel-wired-lan] " Alexander Duyck
2017-11-09  3:12           ` Fengguang Wu
2017-11-09  3:12             ` [Intel-wired-lan] " Fengguang Wu
2017-11-09  4:09             ` Fengguang Wu
2017-11-09  4:09               ` [Intel-wired-lan] " Fengguang Wu
2017-11-09  7:22               ` Fengguang Wu
2017-11-09  7:22                 ` [Intel-wired-lan] " Fengguang Wu
2017-11-09  6:34             ` Cong Wang
2017-11-09  6:34               ` [Intel-wired-lan] " Cong Wang
2017-11-09  6:55               ` Fengguang Wu
2017-11-09  6:55                 ` [Intel-wired-lan] " Fengguang Wu
2017-11-09  7:43                 ` Fengguang Wu
2017-11-09  7:43                   ` [Intel-wired-lan] " Fengguang Wu
2017-11-09 15:51               ` Girish Moodalbail
2017-11-09 15:51                 ` [Intel-wired-lan] " Girish Moodalbail
2017-11-10  0:16                 ` Cong Wang
2017-11-10  0:16                   ` [Intel-wired-lan] " Cong Wang
2017-11-12 19:31         ` Linus Torvalds
2017-11-12 19:31           ` [Intel-wired-lan] " Linus Torvalds
2017-11-13  1:13           ` CONFIG_DEBUG_INFO_SPLIT impacts on faddr2line Fengguang Wu
2017-11-13  1:13             ` [Intel-wired-lan] " Fengguang Wu
2017-11-13  2:05             ` Zhang Rui
2017-11-13  2:05               ` [Intel-wired-lan] " Zhang Rui
2017-11-13  2:22               ` Fengguang Wu
2017-11-13  2:22                 ` [Intel-wired-lan] " Fengguang Wu
2017-11-13 18:52             ` Andi Kleen
2017-11-13 18:52               ` [Intel-wired-lan] " Andi Kleen
2017-11-13 19:14               ` Linus Torvalds
2017-11-13 19:14                 ` [Intel-wired-lan] " Linus Torvalds
2017-11-13 20:10                 ` Andi Kleen
2017-11-13 20:10                   ` [Intel-wired-lan] " Andi Kleen
2017-11-13 20:14                   ` H.J. Lu
2017-11-13 20:14                     ` [Intel-wired-lan] " H.J. Lu
2017-11-13 20:56                   ` Linus Torvalds
2017-11-13 20:56                     ` [Intel-wired-lan] " Linus Torvalds
2017-11-13 21:41                     ` Andi Kleen
2017-11-13 21:41                       ` [Intel-wired-lan] " Andi Kleen
2017-11-13 21:57                       ` Linus Torvalds
2017-11-13 21:57                         ` [Intel-wired-lan] " Linus Torvalds
2017-11-13 23:51                         ` Andi Kleen
2017-11-13 23:51                           ` [Intel-wired-lan] " Andi Kleen
2017-11-14  8:13               ` Fengguang Wu
2017-11-14  8:13                 ` [Intel-wired-lan] " Fengguang Wu
2017-11-09  2:43     ` [vlan_device_event] BUG: unable to handle kernel paging request at 6b6b6ccf Fengguang Wu
2017-11-09  6:48       ` Fengguang Wu

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