xfs: restore buffer_head unwritten bit on ioend cancel
xfs_vm_writepage() walks each buffer_head on the page, maps to the block on disk and attaches to a running ioend structure that represents the I/O submission. A new ioend is created when the type of I/O (unwritten, delayed allocation or overwrite) required for a particular buffer_head differs from the previous. If a buffer_head is a delalloc or unwritten buffer, the associated bits are cleared by xfs_map_at_offset() once the buffer_head is added to the ioend. The process of mapping each buffer_head occurs in xfs_map_blocks() and acquires the ilock in blocking or non-blocking mode, depending on the type of writeback in progress. If the lock cannot be acquired for non-blocking writeback, we cancel the ioend, redirty the page and return. Writeback will revisit the page at some later point. Note that we acquire the ilock for each buffer on the page. Therefore during non-blocking writeback, it is possible to add an unwritten buffer to the ioend, clear the unwritten state, fail to acquire the ilock when mapping a subsequent buffer and cancel the ioend. If this occurs, the unwritten status of the buffer sitting in the ioend has been lost. The page will eventually hit writeback again, but xfs_vm_writepage() submits overwrite I/O instead of unwritten I/O and does not perform unwritten extent conversion at I/O completion. This leads to data corruption because unwritten extents are treated as holes on reads and zeroes are returned instead of reading from disk. Modify xfs_cancel_ioend() to restore the buffer unwritten bit for ioends of type XFS_IO_UNWRITTEN. This ensures that unwritten extent conversion occurs once the page is eventually written back. Signed-off-by: Brian Foster <bfoster@redhat.com> Reviewed-by: Dave Chinner <dchinner@redhat.com> Signed-off-by: Dave Chinner <david@fromorbit.com>
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@ -548,6 +548,13 @@ xfs_cancel_ioend(
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do {
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next_bh = bh->b_private;
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clear_buffer_async_write(bh);
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/*
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* The unwritten flag is cleared when added to the
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* ioend. We're not submitting for I/O so mark the
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* buffer unwritten again for next time around.
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*/
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if (ioend->io_type == XFS_IO_UNWRITTEN)
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set_buffer_unwritten(bh);
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unlock_buffer(bh);
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} while ((bh = next_bh) != NULL);
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