Re: [PATCH 02/25] xfs: invalidate allocbt blocks moved to the free list

Phil White
2012-10-30T17:56:24Z

This looks OK by me.

Reviewed-by: Phil White <pwhite@sgi.com>

On Thu, Oct 25, 2012 at 05:33:51PM +1100, Dave Chinner wrote:
> From: Dave Chinner <dchinner@redhat.com>
>
> When we free a block from the alloc btree tree, we move it to the
> freelist held in the AGFL and mark it busy in the busy extent tree.
> This typically happens when we merge btree blocks.
>
> Once the transaction is committed and checkpointed, the block can
> remain on the free list for an indefinite amount of time. Now, this
> isn't the end of the world at this point - if the free list is
> shortened, the buffer is invalidated in the transaction that moves
> it back to free space. If the buffer is allocated as metadata from
> the free list, then all the modifications getted logged, and we have
> no issues, either. And if it gets allocated as userdata direct from
> the freelist, it gets invalidated and so will never get written.
>
> However, during the time it sits on the free list, pressure on the
> log can cause the AIL to be pushed and the buffer that covers the
> block gets pushed for write. IOWs, we end up writing a freed
> metadata block to disk. Again, this isn't the end of the world
> because we know from the above we are only writing to free space.
>
> The problem, however, is for validation callbacks. If the block was
> on old btree root block, then the level of the block is going to be
> higher than the current tree root, and so will fail validation.
> There may be other inconsistencies in the block as well, and
> currently we don't care because the block is in free space. Shutting
> down the filesystem because a freed block doesn't pass write
> validation, OTOH, is rather unfriendly.
>
> So, make sure we always invalidate buffers as they move from the
> free space trees to the free list so that we guarantee they never
> get written to disk while on the free list.
>
> Signed-off-by: Dave Chinner <dchinner@redhat.com>
> ---
> fs/xfs/xfs_alloc_btree.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/fs/xfs/xfs_alloc_btree.c b/fs/xfs/xfs_alloc_btree.c
> index f1647ca..f7876c6 100644
> --- a/fs/xfs/xfs_alloc_btree.c
> +++ b/fs/xfs/xfs_alloc_btree.c
> @@ -121,6 +121,8 @@ xfs_allocbt_free_block(
> xfs_extent_busy_insert(cur->bc_tp, be32_to_cpu(agf->agf_seqno), bno, 1,
> XFS_EXTENT_BUSY_SKIP_DISCARD);
> xfs_trans_agbtree_delta(cur->bc_tp, -1);
> +
> + xfs_trans_binval(cur->bc_tp, bp);
> return 0;
> }
>
> --
> 1.7.10