Date:	Sun, 05 Aug 2012 10:23:48 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Bernard Pidoux <bernard.pidoux@...e.fr>
Cc:	folkert <folkert@...heusden.com>,
	linux-hams <linux-hams@...r.kernel.org>,
	Linux Netdev List <netdev@...r.kernel.org>
Subject: Re: CPU: 0 Not tainted  (3.1.9+ #1) when ifconfig rose0 down

Bernard Pidoux <bernard.pidoux@...e.fr> writes:

> Thanks for suggesting a bissect. However I guess that this bug has always been
> there !

One thing that has changed recently is I modified
unregister_netdev_notifier to create synthetic events so drivers don't
need a separate network device tear down path in module unload.

For rose it looks like this has triggered latent bugs.

> I am not professionaly involved in programming, however I committed a few
> patches for ROSE, AX.25 and NetRom modules since a few years.
>
> I reactivated netconfig and here is the report showing that kernel panic occurs
> when rose_device_event is triggered when issuing command
> ifconfig rose0 down

Oh ouch!  This is from an ioctl not even at module unload time.

> [ 1215.153302] rose_kill_by_device() rose->neighbour->use 0
> [ 1215.153316] BUG: unable to handle kernel NULL pointer dereference at
> 000000000000002a
> [ 1215.153321] IP: [<ffffffffa065e37d>] rose_device_event+0x11d/0x160 [rose]
> [ 1215.153333] PGD 36340067 PUD 359fa067 PMD 0
> [ 1215.153338] Oops: 0002 [#1] SMP
> [ 1215.153343] CPU 1
> [ 1215.153344] Modules linked in: af_packet rose mkiss ax25 nfsd exportfs nfs
> nfs_acl auth_rpcgss fscache lockd sunrpc netconsole configfs bnep bluetooth
> rfkill snd_hda_codec_idt snd_hda_intel snd_hda_codec snd_hwdep snd_pcm
> snd_page_alloc snd_timer snd i82975x_edac soundcore e1000e ppdev parport_pc
> parport edac_core iTCO_wdt iTCO_vendor_support serio_raw i2c_i801 processor
> coretemp evdev ipv6 autofs4 usbhid hid ext4 crc16 jbd2 sd_mod crc_t10dif
> firewire_ohci firewire_core ehci_hcd crc_itu_t uhci_hcd usbcore usb_common
> nouveau button video mxm_wmi wmi i2c_algo_bit drm_kms_helper ttm drm i2c_core
> ahci libahci ata_piix pata_marvell libata scsi_mod [last unloaded: microcode]
> [ 1215.153395]
> [ 1215.153398] Pid: 18637, comm: ifconfig Not tainted 3.4.7 #8 /D975XBX2
> [ 1215.153404] RIP: 0010:[<ffffffffa065e37d>]  [<ffffffffa065e37d>]
> rose_device_event+0x11d/0x160 [rose]
> [ 1215.153411] RSP: 0000:ffff880035271ca8  EFLAGS: 00010296
> [ 1215.153414] RAX: 0000000000000000 RBX: ffff88003d0c2838 RCX: 0000000230924000
> [ 1215.153417] RDX: 0000000000000002 RSI: 0000000000000001 RDI: ffffffffa0665f28
> [ 1215.153420] RBP: ffff880035271cb8 R08: 0000000000000002 R09: 0000000000000000
> [ 1215.153422] R10: 0000000000000003 R11: 0000000000000000 R12: ffff88003a9e1000
> [ 1215.153425] R13: 00000000fffffff1 R14: ffffffffa05b0000 R15: 0000000000000000
> [ 1215.153429] FS:  00007fb7a318f700(0000) GS:ffff88003fa80000(0000)
> knlGS:0000000000000000
> [ 1215.153433] CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
> [ 1215.153435] CR2: 000000000000002a CR3: 00000000393fd000 CR4: 00000000000007e0
> [ 1215.153438] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> [ 1215.153441] DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
> [ 1215.153445] Process ifconfig (pid: 18637, threadinfo ffff880035270000, task
> ffff88003f5f5d90)
> [ 1215.153448] Stack:
> [ 1215.153450]  0000000000000002 ffff88003a9e1000 ffff880035271cf8
> ffffffff8146d86d
> [ 1215.153455]  ffff880036040d00 0000000000000002 ffff88003a9e1000
> 0000000000000000
> [ 1215.153459]  00000000ffffff9d 0000000000000000 ffff880035271d08
> ffffffff8107a2b6
> [ 1215.153464] Call Trace:
> [ 1215.153470]  [<ffffffff8146d86d>] notifier_call_chain+0x4d/0x70
> [ 1215.153476]  [<ffffffff8107a2b6>] raw_notifier_call_chain+0x16/0x20
> [ 1215.153483]  [<ffffffff81395136>] call_netdevice_notifiers+0x36/0x60
> [ 1215.153487]  [<ffffffff8139b9ea>] __dev_notify_flags+0x6a/0x90
> [ 1215.153491]  [<ffffffff8139ba55>] dev_change_flags+0x45/0x70
> [ 1215.153496]  [<ffffffff81403aed>] devinet_ioctl+0x61d/0x7b0
> [ 1215.153500]  [<ffffffff81403f05>] inet_ioctl+0x75/0x90
> [ 1215.153505]  [<ffffffff8137fbd0>] sock_do_ioctl+0x30/0x70
> [ 1215.153509]  [<ffffffff8137fc89>] sock_ioctl+0x79/0x2f0
> [ 1215.153514]  [<ffffffff811829d8>] do_vfs_ioctl+0x98/0x560
> [ 1215.153517]  [<ffffffff81182f31>] sys_ioctl+0x91/0xa0
> [ 1215.153522]  [<ffffffff81471b39>] system_call_fastpath+0x16/0x1b
> [ 1215.153525] Code: e0 5b 41 5c 31 c0 5d c3 48 8d 7b c8 31 c9 ba 09 00 00 00 be
> 65 00 00 00 e8 a1 5c 00 00 48 8b 83 b8 04 00 00 48 c7 c7 28 5f 66 a0 <66> 83 68
> 2a 01 48 8b 83 b8 04 00 00 0f b7 70 2a 31 c0 e8 d4 10
> [ 1215.153561] RIP  [<ffffffffa065e37d>] rose_device_event+0x11d/0x160 [rose]
> [ 1215.153567]  RSP <ffff880035271ca8>
> [ 1215.153569] CR2: 000000000000002a
> [ 1215.177577] ---[ end trace d23a7ddff228876c ]---
> [ 1215.177589] Kernel panic - not syncing: Fatal exception in interrupt
> [ 1215.177662] panic occurred, switching back to text console
> [ 1215.177717] Rebooting in 60 seconds..
>
> I inserted some printk into rose_device_event() and commented calls to
> subroutines.
> Without calling subroutines, there is no more kernel panic.
> Same results when replacing rose_kill_by_device() in net/rose/af_rose.c,
> rose_link_device_down() and rose_rt_device() in
> net/rose_route.c by a dummy functions with just a printk inside.
>
> I am glad that I found make parameters that shorten the debugging
> cycle :
>
> make modules SUBDIRS=net/rose
> make modules_install SUBDIRS=net/rose
>
> Now I have to go further into each subroutines step by step in order to find out
> the falty code !

Argh inline functions obscuring the backtraces again.

If you are any good at reading assembly you might be able to cut the
tracing time down by using gdb to get a disassembly and looking in the
disassembly.

Although in something easily reproducible what I tend to do is I have
a printk that does.

printk(KERN_EMERG "@%s.%s.%d\n", __FILE__, __func__, __LINE__);

Which I sprinkle all over the code so I know where I fail, and don't
need to cycle too many times.

Sometimes it can be productive to use kvm or a second machine so your
cycle times aren't as long.

In any event I wish you luck tracking this down.

Eric
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