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The iomap direct I/O code issues a single ->end_io call for the whole I/O request, and if some of the extents cowered needed a COW operation it will call xfs_reflink_end_cow over the whole range. When we do AIO writes we drop the iolock after doing the initial setup, but before the I/O completion. Between dropping the lock and completing the I/O we can have a racing buffered write create new delalloc COW fork extents in the region covered by the outstanding direct I/O write, and thus see delalloc COW fork extents in xfs_reflink_end_cow. As concurrent writes are fundamentally racy and no guarantees are given we can simply skip those. This can be easily reproduced with xfstests generic/208 in always_cow mode. Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com> Signed-off-by: Dave Chinner <david@fromorbit.com>
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.
See Documentation/00-INDEX for a list of what is contained in each file.
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.