Re: 2.6.31-rc2: BUG: unable to handle kernel NULL pointer dereference

[Jiri Slaby]

On 07/13/2009 07:00 PM, Thomas Meyer wrote:
>> What warning tainted the kernel before this oops is still interesting...
> 
> There seems to be no OOPS before that BUG. Does a WARNING also set the G
> flag? 

No, W is set by warning. G means no proprietary modules loaded.

> Something like that:
> 
> Jul 12 16:42:34 localhost kernel: [ 6179.647004] ------------[ cut here ]------------
> Jul 12 16:42:34 localhost kernel: [ 6179.647004] WARNING: at lib/kref.c:43 kref_get+0x2f/0x4c()

It tried to get a reference of a structure which was already "freed".
Its reference count already had lowered to 0.

> Jul 12 16:42:34 localhost kernel: [ 6179.647004] Hardware name: MS-7250
> Jul 12 16:42:34 localhost kernel: [ 6179.647004] Modules linked in: rndis_wlan floppy olympic forcedeth [last unloaded: scsi_wait_scan]
> Jul 12 16:42:34 localhost kernel: [ 6179.647004] Pid: 27483, comm: pm-suspend Tainted: G        W  2.6.31-rc2 #79
> Jul 12 16:42:34 localhost kernel: [ 6179.647004] Call Trace:
> Jul 12 16:42:34 localhost kernel: [ 6179.647004]  [<ffffffff8106c1c6>] ? warn_slowpath_common+0x84/0xb2
> Jul 12 16:42:34 localhost kernel: [ 6179.647004]  [<ffffffff8134876b>] ? kref_get+0x2f/0x4c
> Jul 12 16:42:34 localhost kernel: [ 6179.647004]  [<ffffffff813476b2>] ? kobject_get+0x26/0x44
> Jul 12 16:42:34 localhost kernel: [ 6179.647004]  [<ffffffff815a344f>] ? cpufreq_cpu_get+0x74/0xca
> Jul 12 16:42:34 localhost kernel: [ 6179.647004]  [<ffffffff815a3675>] ? cpufreq_suspend+0x5f/0x16f
> Jul 12 16:42:34 localhost kernel: [ 6179.647004]  [<ffffffff81044a4f>] ? disable_local_APIC+0x2d/0x6d
> Jul 12 16:42:34 localhost kernel: [ 6179.647004]  [<ffffffff81449b54>] ? sysdev_suspend+0xa7/0x28d
> Jul 12 16:42:34 localhost kernel: [ 6179.647004]  [<ffffffff810a1229>] ? suspend_devices_and_enter+0x11c/0x1e6
> Jul 12 16:42:34 localhost kernel: [ 6179.647004]  [<ffffffff810a13d8>] ? enter_state+0xe5/0x14c
> Jul 12 16:42:34 localhost kernel: [ 6179.647004]  [<ffffffff810a0841>] ? state_store+0xc1/0xf6
> Jul 12 16:42:34 localhost kernel: [ 6179.647004]  [<ffffffff81178bb8>] ? sysfs_write_file+0xe6/0x137
> Jul 12 16:42:34 localhost kernel: [ 6179.647004]  [<ffffffff81117d03>] ? vfs_write+0xb4/0x126
> Jul 12 16:42:34 localhost kernel: [ 6179.647004]  [<ffffffff81117e5d>] ? sys_write+0x55/0x90
> Jul 12 16:42:34 localhost kernel: [ 6179.647004]  [<ffffffff8102bf2b>] ? system_call_fastpath+0x16/0x1b
> Jul 12 16:42:34 localhost kernel: [ 6179.647004] ---[ end trace f7a4d612974b9b3e ]---
> 
> Btw this seems also to be new in 2.6.31-rc2:

This is unrelated I think. I met it many times.

> Jul 12 16:42:34 localhost kernel: [ 6187.256748] sd 2:0:0:0: [sdb] Starting disk
> Jul 12 16:42:34 localhost kernel: [ 6190.318012] 
> Jul 12 16:42:34 localhost kernel: [ 6190.318128] floppy driver state
> Jul 12 16:42:34 localhost kernel: [ 6190.318244] -------------------
> Jul 12 16:42:34 localhost kernel: [ 6190.320684] now=4300857616 last interrupt=4294760495 diff=6097121 last called handler=ffffffffa00263ea
> Jul 12 16:42:34 localhost kernel: [ 6190.320896] timeout_message=lock fdc
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