xfs: xfs_check_page_type buffer checks need help
xfs_aops_discard_page() was introduced in the following commit: xfs: truncate delalloc extents when IO fails in writeback ... to clean up left over delalloc ranges after I/O failure in ->writepage(). generic/224 tests for this scenario and occasionally reproduces panics on sub-4k blocksize filesystems. The cause of this is failure to clean up the delalloc range on a page where the first buffer does not match one of the expected states of xfs_check_page_type(). If a buffer is not unwritten, delayed or dirty&mapped, xfs_check_page_type() stops and immediately returns 0. The stress test of generic/224 creates a scenario where the first several buffers of a page with delayed buffers are mapped & uptodate and some subsequent buffer is delayed. If the ->writepage() happens to fail for this page, xfs_aops_discard_page() incorrectly skips the entire page. This then causes later failures either when direct IO maps the range and finds the stale delayed buffer, or we evict the inode and find that the inode still has a delayed block reservation accounted to it. We can easily fix this xfs_aops_discard_page() failure by making xfs_check_page_type() check all buffers, but this breaks xfs_convert_page() more than it is already broken. Indeed, xfs_convert_page() wants xfs_check_page_type() to tell it if the first buffers on the pages are of a type that can be aggregated into the contiguous IO that is already being built. xfs_convert_page() should not be writing random buffers out of a page, but the current behaviour will cause it to do so if there are buffers that don't match the current specification on the page. Hence for xfs_convert_page() we need to: a) return "not ok" if the first buffer on the page does not match the specification provided to we don't write anything; and b) abort it's buffer-add-to-io loop the moment we come across a buffer that does not match the specification. Hence we need to fix both xfs_check_page_type() and xfs_convert_page() to work correctly with pages that have mixed buffer types, whilst allowing xfs_aops_discard_page() to scan all buffers on the page for a type match. Reported-by: NBrian Foster <bfoster@redhat.com> Signed-off-by: NDave Chinner <dchinner@redhat.com> Reviewed-by: NChristoph Hellwig <hch@lst.de> Signed-off-by: NDave Chinner <david@fromorbit.com>
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