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    SubjectRe: Dirtiable inode bdi default != sb bdi btrfs
    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@suse.cz>
    > > 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@suse.cz>
    > > ---
    > > 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@suse.cz>
    SUSE Labs, CR


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