xfs: retry COW fork delalloc conversion when no extent was found
While we can only truncate a block under the page lock for the current page, there is no high-level synchronization for moving extents from the COW to the data fork. This means that for example we can have another thread doing a direct I/O completion that moves extents from the COW to the data fork race with writeback. While this race is very hard to hit the always_cow seems to reproduce it reasonably well, and it also exists without that. Because of that there is a chance that a delalloc conversion for the COW fork might not find any extents to convert. In that case we should retry the whole block lookup and now find the blocks in the data fork. Signed-off-by:Christoph Hellwig <hch@lst.de> Reviewed-by:
Darrick J. Wong <darrick.wong@oracle.com> Signed-off-by:
Darrick J. Wong <darrick.wong@oracle.com>
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