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generic/522 (fsx) occasionally fails with a file corruption due to an insert range operation. The primary characteristic of the corruption is a misplaced insert range operation that differs from the requested target offset. The reason for this behavior is a race between the extent shift sequence of an insert range and a COW writeback completion that causes a front merge with the first extent in the shift. The shift preparation function flushes and unmaps from the target offset of the operation to the end of the file to ensure no modifications can be made and page cache is invalidated before file data is shifted. An insert range operation then splits the extent at the target offset, if necessary, and begins to shift the start offset of each extent starting from the end of the file to the start offset. The shift sequence operates at extent level and so depends on the preparation sequence to guarantee no changes can be made to the target range during the shift. If the block immediately prior to the target offset was dirty and shared, however, it can undergo writeback and move from the COW fork to the data fork at any point during the shift. If the block is contiguous with the block at the start offset of the insert range, it can front merge and alter the start offset of the extent. Once the shift sequence reaches the target offset, it shifts based on the latest start offset and silently changes the target offset of the operation and corrupts the file. To address this problem, update the shift preparation code to stabilize the start boundary along with the full range of the insert. Also update the existing corruption check to fail if any extent is shifted with a start offset behind the target offset of the insert range. This prevents insert from racing with COW writeback completion and fails loudly in the event of an unexpected extent shift. Signed-off-by: Brian Foster <bfoster@redhat.com> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.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.