With the recent iomap write page reclaim deadlock fix, it turns out that the
GLF_DIRTY flag isn't always set when it needs to be anymore: previously, this
happened as a side effect of always adding the inode buffer head to the current
transaction with gfs2_trans_add_meta, but this isn't happening consistently
anymore. Fix by removing an additional unnecessary gfs2_trans_add_meta call
and by setting the GLF_DIRTY flag in gfs2_iomap_end.
(The GLF_DIRTY flag causes inode_go_sync to flush the transaction log when
syncing out the glock of that inode. When the flag isn't set, inode_go_sync
will skip inodes, including ones with an i_state of I_DIRTY_PAGES, which will
lead to cluster incoherency.)
In addition, in gfs2_iomap_page_done, if the metadata has changed, mark the
inode as I_DIRTY_DATASYNC to have the inode added to the current transaction:
we don't expect metadata to change here, but let's err on the safe side.