Re: [PATCH v2] tests/xfs: rmapbt swapext block reservation overrun test

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Thu, Feb 08, 2018 at 11:04:29AM -0500, Brian Foster wrote:
> The XFS rmapbt extent swap mechanism performs an extent by extent
> swap to ensure the rmapbt is rectified with the appropriate extent
> owner information after the operation. This implementation suffers
> from a corner case that requires extra reservation if the swap
> operation results in bouncing one of the associated inodes between
> extent and btree formats. When this corner case occurs, it results
> in a transaction block reservation overrun and possible corruption
> of the free space accounting.
> 
> This regression test provides coverage for this corner case. It
> creates two files with a large enough extent count to require btree
> format, regardless of inode size, and performs a sequence of extent
> swaps between them with a decreasing extent count until all extents
> are removed from the file(s). This ensures that one of the swaps
> covers the btree <-> extent fork format boundary case.
> 
> This test reproduces fs corruption on rmapbt enabled filesystems
> running on kernels without the associated extent swap fix.
> 
> Signed-off-by: Brian Foster <bfoster@redhat.com>

Looks ok,
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>

--D