Re: btrfs regression since 4.X kernel NULL pointer dereference

[Stefan Priebe <s.priebe@profihost.ag>]

Am 11.09.2015 um 00:21 schrieb Jeff Mahoney:
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> On 8/31/15 8:06 PM, Chris Mason wrote:
>> On Mon, Aug 31, 2015 at 07:32:09PM +0200, Stefan Priebe -
>> Profihost AG wrote:
>>>> Am 25.08.2015 um 15:51 schrieb Chris Mason <clm@fb.com>:
>>>>
>>>>> On Tue, Aug 25, 2015 at 11:00:30AM +0200, Christoph Hellwig
>>>>> wrote: I think this is btrfs using a struct block_device
>>>>> that doesn't have a valid queue pointer in it's gendisk for
>>>>> ->s_bdev.  And there are some fishy looking ->s_bdev
>>>>> assignments in the code which I suspect are related to it:
>>>>>
>>>>> fs/btrfs/dev-replace.c: if (fs_info->sb->s_bdev ==
>>>>> src_device->bdev) fs/btrfs/dev-replace.c: fs_info->sb->s_bdev
>>>>> = tgt_device->bdev; fs/btrfs/volumes.c: if (device->bdev ==
>>>>> root->fs_info->sb->s_bdev) fs/btrfs/volumes.c:
>>>>> root->fs_info->sb->s_bdev = next_device->bdev;
>>>>> fs/btrfs/volumes.c:     if (tgtdev->bdev ==
>>>>> fs_info->sb->s_bdev) fs/btrfs/volumes.c: fs_info->sb->s_bdev
>>>>> = next_device->bdev;
>>>>
>>>> We've had trouble with this in the past, I'll take a look.
>>>
>>> Any news?
>>
>> Haven't been able to reproduce yet, I'll try again in the morning.
>
> I'm unable to reproduce it as well and I'm hearing about people
> hitting it in different forums.
>
> Can you describe your storage configuration?   There's a gendisk
> without a queue sneaking in somehow.  There are some spots in dm where
> the mddev gets a new queue assigned to it but the old queue associated
> with the gendisk is left behind so that's not it.

I'm hitting this inside a debian buil VM using schroot. So the disk is a 
simple plain qemu emulated scsi disk (virtio-pci-scsi).

 >  If you're able to
> reproduce it reliably with this configuration, that's certainly
> interesting.  I'm wondering if the case is that vgcfgbackup is
> iterating over devices and causing something that might not have been
> previously scanned to be scanned and added to the btrfs device list.

I'm not the guy from the kernel bug report - so i'm only using debian 
schroot not vgcfgbackup.

I can trigger it 100% by using schroot with sbuild using debian or ubuntu.

> Are there any messages above the oops indicating when a device is
> added?  Could you post your complete dmesg somewhere?

Sure:
http://pastebin.com/raw.php?i=bG6bZUPA

Thanks!

Greets,
Stefan

> Thanks,
>
> - -Jeff
>
> - --
> Jeff Mahoney
> SUSE Labs
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