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Brian Foster
f4e4b98cee
Gregg reports that the iomap retry behavior for nonblocking (nowait) append writes is broken. The problem occurs when an append write is first submitted in non-blocking mode (i.e. via io_uring), partially completes before hitting -EAGAIN, and then is resubmitted from blocking context. The specific problem is that at least one iteration of the loop in iomap_write_iter() completes in non-blocking context and thus has bumped i_size. The next iteration hits -EAGAIN, reverts the iov_iter and returns. io_uring retries the entire append write from blocking context, but since i_size has already been increased, the data that was partially written on the first attempt is rewritten at the new i_size. This is essentially an intra-write data corruption since the data written to the file does not reflect the write from userspace. This problem is already fixed on master as of commit1a1a3b574b("iomap: advance the iter directly on buffered writes"). That commit was primarily intended to clean up iomap iter state tracking, but it also happened to remove the iov_iter revert and thus accidentally fix this problem as well. Without the revert, iomap will commit partial progress internally and loop once more before it more than likely hits -EAGAIN and returns partial progress consistent with the inode updates. This means the blocking retry from io_uring will pick up where the first attempt left off at the current i_size and perform the remainder of the write correctly. Cc: <stable@vger.kernel.org> Fixes:18e419f6e8("iomap: Return -EAGAIN from iomap_write_iter()") Reported-by: Gregg Leventhal <gleventhal@janestreet.com> Reported-by: Eric Hagberg <ehagberg@janestreet.com> Signed-off-by: Brian Foster <bfoster@redhat.com> Signed-off-by: Sasha Levin <sashal@kernel.org>
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.