Re: Dirtiable inode bdi default != sb bdi btrfs

From: Artem Bityutskiy <dedekind1@gmail.com>
To: Chris Mason <chris.mason@oracle.com>
Cc: "Jan Kara" <jack@suse.cz>,
	"Cesar Eduardo Barros" <cesarb@cesarb.net>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	hch@lst.de, linux-kernel@vger.kernel.org,
	"Jens Axboe" <jaxboe@fusionio.com>,
	linux-btrfs@vger.kernel.org,
	"Alexander Viro" <viro@zeniv.linux.org.uk>,
	linux-fsdevel@vger.kernel.org, stable@kernel.org,
	"Jens Axboe" <axboe@kernel.dk>,
	"Michał Piotrowski" <mkkp4x4@gmail.com>,
	"Chuck Ebbert" <cebbert@redhat.com>,
	kernel@lists.fedoraproject.org
Subject: Re: Dirtiable inode bdi default != sb bdi btrfs
Date: Tue, 28 Sep 2010 10:05:49 +0300	[thread overview]
Message-ID: <1285657549.2437.28.camel@localhost> (raw)
In-Reply-To: <20100927225452.GG4270@think>

On Mon, 2010-09-27 at 18:54 -0400, Chris Mason wrote:
> On Tue, Sep 28, 2010 at 12:25:48AM +0200, Jan Kara wrote:
> > [Added CCs for similar ecryptfs warning]
> > On Thu 23-09-10 12:38:49, Andrew Morton wrote:
> > > > This started appearing for me on v2.6.36-rc5-49-gc79bd89; it di=
d not=20
> > > > happen on v2.6.36-rc5-33-g1ce1e41, probably because it does not=
 have=20
> > > > commit 692ebd17c2905313fff3c504c249c6a0faad16ec which introduce=
s the=20
> > > > warning.
> > > > [...]
> > > > device fsid 44d595920ddedfa-3ece6b56e80f689e devid 1 transid 22=
342=20
> > > > /dev/mapper/vg_cesarbinspiro-lv_home
> > > > SELinux: initialized (dev dm-3, type btrfs), uses xattr
> > > > ------------[ cut here ]------------
> > > > WARNING: at fs/fs-writeback.c:87 inode_to_bdi+0x62/0x6d()
> > > > Hardware name: Inspiron N4010
> > > > Dirtiable inode bdi default !=3D sb bdi btrfs
> > > > Modules linked in: ipv6 kvm_intel kvm uinput arc4 ecb=20
> > > > snd_hda_codec_intelhdmi snd_hda_codec_realtek iwlagn snd_hda_in=
tel=20
> > > > iwlcore snd_hda_codec uvcvideo snd_hwdep mac80211 videodev snd_=
seq=20
> > > > snd_seq_device v4l1_compat snd_pcm atl1c v4l2_compat_ioctl32 bt=
usb=20
> > > > cfg80211 snd_timer i2c_i801 bluetooth iTCO_wdt dell_wmi dell_la=
ptop snd=20
> > > > pcspkr wmi dcdbas shpchp iTCO_vendor_support soundcore snd_page=
_alloc=20
> > > > rfkill joydev microcode btrfs zlib_deflate libcrc32c cryptd aes=
_x86_64=20
> > > > aes_generic xts gf128mul dm_crypt usb_storage i915 drm_kms_help=
er drm=20
> > > > i2c_algo_bit i2c_core video output [last unloaded: scsi_wait_sc=
an]
> > > > Pid: 1073, comm: find Not tainted 2.6.36-rc5+ #8
> > > > Call Trace:
> > > >   [<ffffffff8104d0e4>] warn_slowpath_common+0x85/0x9d
> > > >   [<ffffffff8104d19f>] warn_slowpath_fmt+0x46/0x48
> > > >   [<ffffffff811308b7>] inode_to_bdi+0x62/0x6d
> > > >   [<ffffffff81131b48>] __mark_inode_dirty+0xd0/0x177
> > > >   [<ffffffff81127168>] touch_atime+0x107/0x12a
> > > >   [<ffffffff81122384>] ? filldir+0x0/0xd0
> > > >   [<ffffffff8112259b>] vfs_readdir+0x8d/0xb4
> > > >   [<ffffffff8112270b>] sys_getdents+0x81/0xd1
> > > >   [<ffffffff81009c72>] system_call_fastpath+0x16/0x1b
> >   Thanks for the report. These bdi pointers are a mess. As Chris po=
inted
> > out, btrfs forgets to properly initialize inode->i_mapping.backing_=
dev_info
> > for directories and special inodes and thus these were previously a=
ttached
> > to default_backing_dev_info which probably isn't what Chris would l=
ike to
> > see.
>=20
> There's no actual writeback for these, so it works fine for btrfs eit=
her
> way.

Side note: every time inode is marked as dirty, we wake up a bdi thread
or the default bdi thread. So if we have inodes which do not need
write-back, we should never mark them as dirty.

--=20
Best Regards,
Artem Bityutskiy (=D0=90=D1=80=D1=82=D1=91=D0=BC =D0=91=D0=B8=D1=82=D1=8E=
=D1=86=D0=BA=D0=B8=D0=B9)