On Thu, Aug 28, 2014 at 09:49:10PM +1000, Dave Chinner wrote: > From: Dave Chinner <dchinner@xxxxxxxxxx> > > If we have delalloc extents on a file before we run a collapse range > opertaion, we sync the range that we are going to collapse to > convert delalloc extents in that region to real extents to simplify > the shift operation. > > However, the shift operation then assumes that the extent list is > not going to change as it iterates over the extent list moving > things about. Unfortunately, this isn't true because we can't hold > the ILOCK over all the operations. We can prevent new IO from > modifying the extent list by holding the IOLOCK, but that doesn't > prevent writeback from running.... > > And when writeback runs, it can convert delalloc extents is the > range of the file prior to the region being collapsed, and this > changes the indexes of all the extents in the file. That causes the > collapse range operation to Go Bad. > > The right fix is to rewrite the extent shift operation not to be > dependent on the extent list not changing across the entire > operation, but this is a fairly significant piece of work to do. > Hence, as a short-term workaround for the problem, sync the entire > file before starting a collapse operation to remove all delalloc > ranges from the file and so avoid the problem of concurrent > writeback changing the extent list. > > Diagnosed-and-Reported-by: Brian Foster <bfoster@xxxxxxxxxx> > Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx> > Reviewed-by: Brian Foster <bfoster@xxxxxxxxxx> Looks good, Reviewed-by: Christoph Hellwig <hch@xxxxxx> _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
