libxfs: reused invalidated buffers leak state and data

libxfs: reused invalidated buffers leak state and data

When rebuilding a bad directory, repair first truncates away all the
blocks in the directory, good or bad. This removes blocks from the
bmap btree, and when those blocks are freed the bmap btree code
invalidates them. This marks the buffers LIBXFS_B_STALE so that we
don't try to write stale data from that buffer at a later time.

However, when rebuilding the directory, blocks may get reallocated
and we reuse the underlying buffers. This has two problems.

The first is that if the buffer was previously detected as having a
verifier error (i.e. an error that is leading to the block being
freed and the buffer being invalidated) then the error might still
be held in b_error. Hence the libxfs code needs to ensure that
b_error does not leak from one buffer usage context to another
after invalidation.

The second problem is that when new data is written into a buffer,
it no longer has stale contents. Hence when we write the buffer, we
need to clear the LIBXFS_B_STALE flag to ensure that the new data
gets written.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>