Re: Dirtiable inode bdi default != sb bdi btrfs

[Chris Mason]

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.

>   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.

-chris

> 
> 								Honza
> -- 
> Jan Kara <jack@xxxxxxx>
> SUSE Labs, CR
> ---
> 
> 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
> 
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