ceph: don't use writeback_control in writepages completion

The ->writepages writeback_control is not still valid in the writepages
completion.  We were touching it solely to adjust pages_skipped when there
was a writeback error (EIO, ENOSPC, EPERM due to bad osd credentials),
causing an oops in the writeback code shortly thereafter.  Updating
pages_skipped on error isn't correct anyway, so let's just rip out this
(clearly broken) code to pass the wbc to the completion.
Signed-off-by: Sage Weil <sage@newdream.net>

fs/ceph/addr.c

@@ -504,7 +504,6 @@ static void writepages_finish(struct ceph_osd_request *req,
 	int i;
 	struct ceph_snap_context *snapc = req->r_snapc;
 	struct address_space *mapping = inode->i_mapping;
-	struct writeback_control *wbc = req->r_wbc;
 	__s32 rc = -EIO;
 	u64 bytes = 0;
 	struct ceph_client *client = ceph_inode_to_client(inode);
@@ -546,10 +545,6 @@ static void writepages_finish(struct ceph_osd_request *req,
 			clear_bdi_congested(&client->backing_dev_info,
 					    BLK_RW_ASYNC);
 
-		if (i >= wrote) {
-			dout("inode %p skipping page %p\n", inode, page);
-			wbc->pages_skipped++;
-		}
 		ceph_put_snap_context((void *)page->private);
 		page->private = 0;
 		ClearPagePrivate(page);
@@ -799,7 +794,6 @@ static int ceph_writepages_start(struct address_space *mapping,
 				alloc_page_vec(client, req);
 				req->r_callback = writepages_finish;
 				req->r_inode = inode;
-				req->r_wbc = wbc;
 			}
 
 			/* note position of first page in pvec */

fs/ceph/osd_client.h

@@ -66,7 +66,6 @@ struct ceph_osd_request {
 	struct list_head  r_unsafe_item;
 
 	struct inode *r_inode;         	      /* for use by callbacks */
-	struct writeback_control *r_wbc;      /* ditto */
 
 	char              r_oid[40];          /* object name */
 	int               r_oid_len;