GFS2: Fix bmap allocation corner-case bug

commit 07ccb7bf upstream.

This patch solves a corner case during allocation which occurs if both
metadata (indirect) and data blocks are required but there is an
obstacle in the filesystem (e.g. a resource group header or another
allocated block) such that when the allocation is requested only
enough blocks for the metadata are returned.

By changing the exit condition of this loop, we ensure that a
minimum of one data block will always be returned.
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
Cc: maximilian attems <max@stro.at>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

fs/gfs2/bmap.c

@@ -541,7 +541,7 @@ static int gfs2_bmap_alloc(struct inode *inode, const sector_t lblock,
 				*ptr++ = cpu_to_be64(bn++);
 			break;
 		}
-	} while (state != ALLOC_DATA);
+	} while ((state != ALLOC_DATA) || !dblock);
 
 	ip->i_height = height;
 	gfs2_add_inode_blocks(&ip->i_inode, alloced);