From mboxrd@z Thu Jan  1 00:00:00 1970
From: Maciej Marcin Piechotka <uzytkownik2@gmail.com>
Subject: Re: Regression in btrfs-next: BUG at fs/btrfs/super.c:984!
Date: Sun, 02 Oct 2011 23:15:33 +0200
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On Sun, 2011-10-02 at 19:39 +0200, David Sterba wrote:
> On Sat, Oct 01, 2011 at 11:43:10PM +0200, Maciej Marcin Piechotka wrote:
> > PS. It might happened that it was caused by parition mounted read-only
> > on read-only block device.
>   ^^^
>=20
> This is the key information!
>=20
> super.c: btrfs_calc_avail_data_space()
>  983         nr_devices =3D fs_info->fs_devices->rw_devices;
>  984         BUG_ON(!nr_devices);
>=20
>=20
> If there are no writable devices, this BUGON fires, although this case
> in connection with RO mount is handled elsewhere properly.
>=20
> This is called through sysfs and just tries to obtain available free
> space information to print it. I think the BUG_ON is not necessary here
> and the function can take a short track returning 0 as available free
> space:
>=20
> if (!nr_devices) {
> 	*free_bytes =3D 0;
> 	return 0;
> }
>=20
> I could be possible to actually read the free space even from a RO
> device (be it RO mount or not), but I don't see much benefit which would
> justify the work.
>=20
> Can you please test the fix and let us know if the statfs number look
> reasonable?
>=20
>=20
> david

Well - it shows size 50G, used 29G and avail 0G in df -h.

Regards

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