libxfs: don't repeatedly shake unwritable buffers

libxfs: don't repeatedly shake unwritable buffers

now that we try to write dirty buffers before we release them, we
can get buildup of unwritable dirty buffers on the LRU lists, This
results in the cache shaker repeatedly trying to write out these
buffers every time the cache fills up. This results in more
corruption warnings, and takes up a lot of time doing reclaiming
nothing. This can effectively livelock the processing parts of phase
4.

Fix this by not trying to write buffers with corruption errors on
them. These errors will get cleared when the buffer is re-read and
fixed and them marked dirty again. At which point, we'll be able to
write them and so the cache can reclaim them successfully.

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