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If we are doing NOWAIT direct IO read/write and our inode has compressed extents, we call filemap_fdatawrite_range() against the range in order to wait for compressed writeback to complete, since the generic code at iomap_dio_rw() calls filemap_write_and_wait_range() once, which is not enough to wait for compressed writeback to complete. This call to filemap_fdatawrite_range() can block on page locks, since the first writepages() on a range that we will try to compress results only in queuing a work to compress the data while holding the pages locked. Even though the generic code at iomap_dio_rw() will do the right thing and return -EAGAIN for NOWAIT requests in case there are pages in the range, we can still end up at btrfs_dio_iomap_begin() with pages in the range because either of the following can happen: 1) Memory mapped writes, as we haven't locked the range yet; 2) Buffered reads might have started, which lock the pages, and we do the filemap_fdatawrite_range() call before locking the file range. So don't call filemap_fdatawrite_range() at btrfs_dio_iomap_begin() if we are doing a NOWAIT read/write. Instead call filemap_range_needs_writeback() to check if there are any locked, dirty, or under writeback pages, and return -EAGAIN if that's the case. Signed-off-by: Filipe Manana <fdmanana@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.