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350976ae21
On truncate down, if new size is not block size aligned, we zero the rest of block to avoid exposing stale data to user, and iomap_truncate_page() skips zeroing if the range is already in unwritten state or a hole. Then we writeback from on-disk i_size to the new size if this range hasn't been written to disk yet, and truncate page cache beyond new EOF and set in-core i_size. The problem is that we could write data between di_size and newsize before removing the page cache beyond newsize, as the extents may still be in unwritten state right after a buffer write. As such, the page of data that newsize lies in has not been zeroed by page cache invalidation before it is written, and xfs_do_writepage() hasn't triggered it's "zero data beyond EOF" case because we haven't updated in-core i_size yet. Then a subsequent mmap read could see non-zeros past EOF. I occasionally see this in fsx runs in fstests generic/112, a simplified fsx operation sequence is like (assuming 4k block size xfs): fallocate 0x0 0x1000 0x0 keep_size write 0x0 0x1000 0x0 truncate 0x0 0x800 0x1000 punch_hole 0x0 0x800 0x800 mapread 0x0 0x800 0x800 where fallocate allocates unwritten extent but doesn't update i_size, buffer write populates the page cache and extent is still unwritten, truncate skips zeroing page past new EOF and writes the page to disk, punch_hole invalidates the page cache, at last mapread reads the block back and sees non-zero beyond EOF. Fix it by moving truncate_setsize() to before writeback so the page cache invalidation zeros the partial page at the new EOF. This also triggers "zero data beyond EOF" in xfs_do_writepage() at writeback time, because newsize has been set and page straddles the newsize. Also fixed the wrong 'end' param of filemap_write_and_wait_range() call while we're at it, the 'end' is inclusive and should be 'newsize - 1'. Suggested-by: Dave Chinner <dchinner@redhat.com> Signed-off-by: Eryu Guan <eguan@redhat.com> Acked-by: Dave Chinner <dchinner@redhat.com> 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> |
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. 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.