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> --- fs/xfs/xfs_bmap_util.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c index c53cc03..035041d 100644 --- a/fs/xfs/xfs_bmap_util.c +++ b/fs/xfs/xfs_bmap_util.c @@ -1460,6 +1460,19 @@ xfs_collapse_file_space( start_fsb = XFS_B_TO_FSB(mp, offset + len); shift_fsb = XFS_B_TO_FSB(mp, len); + /* + * writeback the entire file to prevent concurrent writeback of ranges + * outside the collapsing region from changing the extent list. + * + * XXX: This is a temporary fix until the extent shift loop below is + * converted to use offsets and lookups within the ILOCK rather than + * carrying around the index into the extent list for the next + * iteration. + */ + error = filemap_write_and_wait(VFS_I(ip)->i_mapping); + if (error) + return error; + error = xfs_free_file_space(ip, offset, len); if (error) return error; -- 2.0.0 _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
