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From: Josef Bacik <josef@toxicpanda.com>
To: linux-btrfs@vger.kernel.org, kernel-team@fb.com
Subject: [RFC][PATCH 0/5] btrfs: fix hole corruption issue with !NO_HOLES
Date: Mon, 30 Dec 2019 16:31:13 -0500
Message-ID: <20191230213118.7532-1-josef@toxicpanda.com> (raw)

We've historically had this problem where you could flush a targeted section of
an inode and end up with a hole between extents without a hole extent item.
This of course makes fsck complain because this is not ok for a file system that
doesn't have NO_HOLES set.  Because this is a well understood problem I and
others have been ignoring fsck failures during certain xfstests (generic/475 for
example) because they would regularly trigger this edge case.

However this isn't a great behavior to have, we should really be taking all fsck
failures seriously, and we could potentially ignore fsck legitimate fsck errors
because we expect it to be this particular failure.

In order to fix this we need to keep track of where we have valid extent items,
and only update i_size to encompass that area.  This unfortunately means we need
a new per-inode extent_io_tree to keep track of the valid ranges.  This is
relatively straightforward in practice, and helpers have been added to manage
this so that in the case of a NO_HOLES file system we just simply skip this work
altogether.

I've been hammering on this for a week now and I'm pretty sure its ok, but I'd
really like Filipe to take a look and I still have some longer running tests
going on the series.  All of our boxes internally are btrfs and the box I was
testing on ended up with a weird RPM db corruption that was likely from an
earlier, broken version of the patch.  However I cannot be 100% sure that was
the case, so I'm giving it a few more days of testing before I'm satisfied
there's not some weird thing that RPM does that xfstests doesn't cover.

This has gone through several iterations of xfstests already, including many
loops of generic/475 for validation to make sure it was no longer failing.  So
far so good, but for something like this wider testing will definitely be
necessary.  Thanks,

Josef


             reply index

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-30 21:31 Josef Bacik [this message]
2019-12-30 21:31 ` [PATCH 1/5] btrfs: use btrfs_ordered_update_i_size in clone_finish_inode_update Josef Bacik
2019-12-30 21:31 ` [PATCH 2/5] btrfs: introduce the inode->file_extent_tree Josef Bacik
2020-01-06 17:22   ` David Sterba
2020-01-06 19:29     ` Josef Bacik
2020-01-07 16:17       ` David Sterba
2020-01-07 16:45         ` Filipe Manana
2020-01-07 16:46   ` David Sterba
2019-12-30 21:31 ` [PATCH 3/5] btrfs: use the file extent tree infrastructure Josef Bacik
2019-12-30 21:31 ` [PATCH 4/5] btrfs: replace all uses of btrfs_ordered_update_i_size Josef Bacik
2019-12-30 21:31 ` [PATCH 5/5] btrfs: delete the ordered isize update code Josef Bacik
2019-12-31 12:25 ` [RFC][PATCH 0/5] btrfs: fix hole corruption issue with !NO_HOLES Qu Wenruo
2020-01-02 16:10   ` Josef Bacik

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