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[ Upstream commit 249bd9087a5264d2b8a974081870e2e27671b4dc ] AIO+DIO can extend the file size on IO completion, and it holds no inode locks while the IO is in flight. Therefore, a race condition exists in file size updates if we do something like this: aio-thread fallocate-thread lock inode submit IO beyond inode->i_size unlock inode ..... lock inode break layouts if (off + len > inode->i_size) new_size = off + len ..... inode_dio_wait() <blocks> ..... completes inode->i_size updated inode_dio_done() .... <wakes> <does stuff no long beyond EOF> if (new_size) xfs_vn_setattr(inode, new_size) Yup, that attempt to extend the file size in the fallocate code turns into a truncate - it removes the whatever the aio write allocated and put to disk, and reduced the inode size back down to where the fallocate operation ends. Fundamentally, xfs_file_fallocate() not compatible with racing AIO+DIO completions, so we need to move the inode_dio_wait() call up to where the lock the inode and break the layouts. Secondly, storing the inode size and then using it unchecked without holding the ILOCK is not safe; we can only do such a thing if we've locked out and drained all IO and other modification operations, which we don't do initially in xfs_file_fallocate. It should be noted that some of the fallocate operations are compound operations - they are made up of multiple manipulations that may zero data, and so we may need to flush and invalidate the file multiple times during an operation. However, we only need to lock out IO and other space manipulation operations once, as that lockout is maintained until the entire fallocate operation has been completed. Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-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> Signed-off-by: Sasha Levin <sashal@kernel.org> |
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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.