ext4: fix xfstest generic/269 double revoked buffer bug with bigalloc

When you repeatly execute xfstest generic/269 with bigalloc_1k option
enabled using the below command:

"./kvm-xfstests -c bigalloc_1k -m nodelalloc -C 1000 generic/269"

you can easily see the below bug message.

"JBD2 unexpected failure: jbd2_journal_revoke: !buffer_revoked(bh);"

This means that an already revoked buffer is erroneously revoked again
and it is caused by doing revoke for the buffer at the wrong position
in ext4_free_blocks(). We need to re-position the buffer revoke
procedure for an unspecified buffer after checking the cluster boundary
for bigalloc option. If not, some part of the cluster can be doubly
revoked.
Signed-off-by: NDaeho Jeong <daeho.jeong@samsung.com>

fs/ext4/mballoc.c

@@ -4687,22 +4687,11 @@ void ext4_free_blocks(handle_t *handle, struct inode *inode,
 	ext4_debug("freeing block %llu\n", block);
 	trace_ext4_free_blocks(inode, block, count, flags);
 
-	if (flags & EXT4_FREE_BLOCKS_FORGET) {
-		struct buffer_head *tbh = bh;
-		int i;
-
-		BUG_ON(bh && (count > 1));
+	if (bh && (flags & EXT4_FREE_BLOCKS_FORGET)) {
+		BUG_ON(count > 1);
 
-		for (i = 0; i < count; i++) {
-			cond_resched();
-			if (!bh)
-				tbh = sb_find_get_block(inode->i_sb,
-							block + i);
-			if (!tbh)
-				continue;
-			ext4_forget(handle, flags & EXT4_FREE_BLOCKS_METADATA,
-				    inode, tbh, block + i);
-		}
+		ext4_forget(handle, flags & EXT4_FREE_BLOCKS_METADATA,
+			    inode, bh, block);
 	}
 
 	/*
@@ -4747,6 +4736,19 @@ void ext4_free_blocks(handle_t *handle, struct inode *inode,
 			count += sbi->s_cluster_ratio - overflow;
 	}
 
+	if (!bh && (flags & EXT4_FREE_BLOCKS_FORGET)) {
+		int i;
+
+		for (i = 0; i < count; i++) {
+			cond_resched();
+			bh = sb_find_get_block(inode->i_sb, block + i);
+			if (!bh)
+				continue;
+			ext4_forget(handle, flags & EXT4_FREE_BLOCKS_METADATA,
+				    inode, bh, block + i);
+		}
+	}
+
 do_more:
 	overflow = 0;
 	ext4_get_group_no_and_offset(sb, block, &block_group, &bit);