ceph: fix -EOLDSNAPC handling

Need to drop cap reference before retry. Besides, it's better to
redo file write checks for each retry because we re-lock inode.
Signed-off-by: N"Yan, Zheng" <zyan@redhat.com>
Signed-off-by: NIlya Dryomov <idryomov@gmail.com>

fs/ceph/file.c

@@ -1309,6 +1309,7 @@ static ssize_t ceph_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	if (!prealloc_cf)
 		return -ENOMEM;
 
+retry_snap:
 	inode_lock(inode);
 
 	/* We can write back this queue in page reclaim */
@@ -1340,7 +1341,6 @@ static ssize_t ceph_write_iter(struct kiocb *iocb, struct iov_iter *from)
 			goto out;
 	}
 
-retry_snap:
 	/* FIXME: not complete since it doesn't account for being at quota */
 	if (ceph_osdmap_flag(osdc, CEPH_OSDMAP_FULL)) {
 		err = -ENOSPC;
@@ -1389,14 +1389,6 @@ static ssize_t ceph_write_iter(struct kiocb *iocb, struct iov_iter *from)
 							 &prealloc_cf);
 		else
 			written = ceph_sync_write(iocb, &data, pos, snapc);
-		if (written == -EOLDSNAPC) {
-			dout("aio_write %p %llx.%llx %llu~%u"
-				"got EOLDSNAPC, retrying\n",
-				inode, ceph_vinop(inode),
-				pos, (unsigned)count);
-			inode_lock(inode);
-			goto retry_snap;
-		}
 		if (written > 0)
 			iov_iter_advance(from, written);
 		ceph_put_snap_context(snapc);
@@ -1430,10 +1422,15 @@ static ssize_t ceph_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	     ceph_cap_string(got));
 	ceph_put_cap_refs(ci, got);
 
+	if (written == -EOLDSNAPC) {
+		dout("aio_write %p %llx.%llx %llu~%u" "got EOLDSNAPC, retrying\n",
+		     inode, ceph_vinop(inode), pos, (unsigned)count);
+		goto retry_snap;
+	}
+
 	if (written >= 0) {
 		if (ceph_osdmap_flag(osdc, CEPH_OSDMAP_NEARFULL))
 			iocb->ki_flags |= IOCB_DSYNC;
-
 		written = generic_write_sync(iocb, written);
 	}