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Date: Mon, 28 Jan 2013 18:11:08 +0200
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Subject: backref for an extent not found in send_root (!backref_ctx->found_itself)
From: Alex Lyakas <alex.btrfs@zadarastorage.com>
To: Jan Schmidt <list.btrfs@jan-o-sch.net>,
        linux-btrfs <linux-btrfs@vger.kernel.org>
Cc: Arne Jansen <sensille@gmx.net>, Alexander Block <ablock84@googlemail.com>
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Hi Jan,
I have a set of unit tests (part of the larger system) for the
send-receive functionality, with which I am able to hit this error:

Jan 28 18:01:00 687-dev kernel: [16968.451358] btrfs: ERROR did not
find backref in send_root. inode=259, offset=139264, disk_byte=4263936
found extent=4263936

As the code states, this could indicate a bug in backref walking. This
reproduces with "for-linus" branch.

Typically this happens when a snapshot is deleted, immediately a new
snap with the same name is created, and then "btrfs send" is issued
without parent (i.e., full-send) on this snap.

To debug this further, we can do one of two things:
# I can apply patches/debug prints & reproduce
# I can work to isolate the unit test into a bash script and send you
a script that reproduces

Please let me know.

Thanks,
Alex.