Re: Dirtiable inode bdi default != sb bdi btrfs

[Jan Kara]

On Mon 27-09-10 18:54:52, 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 did not 
> > > > happen on v2.6.36-rc5-33-g1ce1e41, probably because it does not have 
> > > > commit 692ebd17c2905313fff3c504c249c6a0faad16ec which introduces the 
> > > > warning.
> > > > [...]
> > > > device fsid 44d595920ddedfa-3ece6b56e80f689e devid 1 transid 22342 
> > > > /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 != sb bdi btrfs
> > > > Modules linked in: ipv6 kvm_intel kvm uinput arc4 ecb 
> > > > snd_hda_codec_intelhdmi snd_hda_codec_realtek iwlagn snd_hda_intel 
> > > > iwlcore snd_hda_codec uvcvideo snd_hwdep mac80211 videodev snd_seq 
> > > > snd_seq_device v4l1_compat snd_pcm atl1c v4l2_compat_ioctl32 btusb 
> > > > cfg80211 snd_timer i2c_i801 bluetooth iTCO_wdt dell_wmi dell_laptop snd 
> > > > pcspkr wmi dcdbas shpchp iTCO_vendor_support soundcore snd_page_alloc 
> > > > rfkill joydev microcode btrfs zlib_deflate libcrc32c cryptd aes_x86_64 
> > > > aes_generic xts gf128mul dm_crypt usb_storage i915 drm_kms_helper drm 
> > > > i2c_algo_bit i2c_core video output [last unloaded: scsi_wait_scan]
> > > > 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 pointed
> > out, btrfs forgets to properly initialize inode->i_mapping.backing_dev_info
> > for directories and special inodes and thus these were previously attached
> > to default_backing_dev_info which probably isn't what Chris would like to
> > see.
> 
> There's no actual writeback for these, so it works fine for btrfs either
> way.
  Ah, OK. I see you do all the writing already at inode dirtying time so
you don't really care what happens after the dirtying for inodes without
page cache. So it's really just a cosmetic issue for btrfs.

> >   I've also got a similar report for ecryptfs which also does not
> > initialize inode->i_mapping.backing_dev_info although it sets sb->s_bdi and
> > thus again its inodes get filed to default_backing_dev_info lists.  Quick
> > search seems to reveal that other filesystems using handcrafted bdi's get
> > it wrong as well and thus their inodes end up in the default_backing_dev_info
> > lists which is generally undesirable (this was happening already before my
> > patch, my code just started complaining about that).
> >   That suggests that we should probably handle such cases in a more generic
> > way by changing the code in inode_init_always(). The patch below makes at
> > least btrfs happy for me... Could you maybe test it? Thanks.
> 
> Christoph had a slightly different plan for this, I've cc'd him and kept
> the patch below for comment.
  OK, thanks.

								Honza
> > ---
> > 
> > From 29f60c2b08ff9637a10439d1513805835ddcc746 Mon Sep 17 00:00:00 2001
> > From: Jan Kara <jack@xxxxxxx>
> > Date: Mon, 27 Sep 2010 23:56:48 +0200
> > Subject: [PATCH] bdi: Initialize inode->i_mapping.backing_dev_info to sb->s_bdi
> > 
> > Currently, we initialize inode->i_mapping.backing_dev_info to the bdi of device
> > sb->s_bdev points to. However there is quite a big number of filesystems that
> > do not set sb->s_bdev (because they do not have one) but do set sb->s_bdi.
> > These filesystems would generally benefit from setting
> > inode->i_mapping.backing_dev_info to their s_bdi because otherwise their inodes
> > would point to default_backing_dev_info and thus dirty inode tracking would
> > happen there. So change inode initialization code to use sb->s_bdi if it
> > is available.
> > 
> > Signed-off-by: Jan Kara <jack@xxxxxxx>
> > ---
> >  fs/inode.c |   22 ++++++++++++++--------
> >  1 files changed, 14 insertions(+), 8 deletions(-)
> > 
> > diff --git a/fs/inode.c b/fs/inode.c
> > index 8646433..e415be4 100644
> > --- a/fs/inode.c
> > +++ b/fs/inode.c
> > @@ -172,15 +172,21 @@ int inode_init_always(struct super_block *sb, struct inode *inode)
> >  	mapping->writeback_index = 0;
> >  
> >  	/*
> > -	 * If the block_device provides a backing_dev_info for client
> > -	 * inodes then use that.  Otherwise the inode share the bdev's
> > -	 * backing_dev_info.
> > +	 * If the filesystem provides a backing_dev_info for client inodes
> > +	 * then use that. Otherwise inodes share default_backing_dev_info.
> >  	 */
> > -	if (sb->s_bdev) {
> > -		struct backing_dev_info *bdi;
> > -
> > -		bdi = sb->s_bdev->bd_inode->i_mapping->backing_dev_info;
> > -		mapping->backing_dev_info = bdi;
> > +	if (sb->s_bdi && sb->s_bdi != &noop_backing_dev_info) {
> > +		/*
> > +		 * Catch cases where filesystem might be bitten by using s_bdi
> > +		 * instead of sb->s_bdev. Can be removed in 2.6.38.
> > +		 */
> > +		if (sb->s_bdev) {
> > +			struct backing_dev_info *bdi =
> > +			  sb->s_bdev->bd_inode->i_mapping->backing_dev_info;
> > +			WARN(bdi != sb->s_bdi, "s_bdev bdi %s != s_bdi %s\n",
> > +			     bdi->name, sb->s_bdi->name);
> > +		}
> > +		mapping->backing_dev_info = sb->s_bdi;
> >  	}
> >  	inode->i_private = NULL;
> >  	inode->i_mapping = mapping;
> > -- 
> > 1.6.4.2
> > 
-- 
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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