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The existing comments in btrfs_invalidatepage() don't really get to the point, especially for what Private2 is really representing and how the race avoidance is done. The truth is, there are only three entrances to do ordered extent accounting: - btrfs_writepage_endio_finish_ordered() - __endio_write_update_ordered() Those two entrance are just endio functions for dio and buffered write. - btrfs_invalidatepage() But there is a pitfall, in endio functions there is no check on whether the ordered extent is already accounted. They just blindly clear the Private2 bit and do the accounting. So it's all btrfs_invalidatepage()'s responsibility to make sure we won't do double account for the same sector. That's why in btrfs_invalidatepage() we have to wait for page writeback, this will ensure all submitted bios have finished, thus their endio functions have finished the accounting on the ordered extent. Then we also check page Private2 to ensure that, we only run ordered extent accounting on pages who has no bio submitted. This patch will rework related comments to make it more clear on the race and how we use wait_on_page_writeback() and Private2 to prevent double accounting on ordered extent. Reviewed-by: Josef Bacik <josef@toxicpanda.com> Signed-off-by: Qu Wenruo <wqu@suse.com> Signed-off-by: David Sterba <dsterba@suse.com> |
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.