nilfs2: fix kernel oops in error case of nilfs_ioctl_move_blocks

This fixes a kernel oops reported by Markus Trippelsdorf in the email
titled "[NILFS users] kernel Oops while running nilfs_cleanerd".

The oops was caused by a bug of error path in
nilfs_ioctl_move_blocks() function, which was inlined in
nilfs_ioctl_clean_segments().

nilfs_ioctl_move_blocks checks duplication of blocks which will be
moved in garbage collection.  But, the check should have be done
within nilfs_ioctl_move_inode_block() to prevent list corruption among
buffers storing the target blocks.

To fix the kernel oops, this moves forward the duplication check
before the list insertion.

I also tested this for stable trees [2.6.30, 2.6.31].
Reported-by: NMarkus Trippelsdorf <markus@trippelsdorf.de>
Signed-off-by: NRyusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Cc: stable <stable@kernel.org>

fs/nilfs2/ioctl.c

@@ -297,7 +297,18 @@ static int nilfs_ioctl_move_inode_block(struct inode *inode,
 			       (unsigned long long)vdesc->vd_vblocknr);
 		return ret;
 	}
-	bh->b_private = vdesc;
+	if (unlikely(!list_empty(&bh->b_assoc_buffers))) {
+		printk(KERN_CRIT "%s: conflicting %s buffer: ino=%llu, "
+		       "cno=%llu, offset=%llu, blocknr=%llu, vblocknr=%llu\n",
+		       __func__, vdesc->vd_flags ? "node" : "data",
+		       (unsigned long long)vdesc->vd_ino,
+		       (unsigned long long)vdesc->vd_cno,
+		       (unsigned long long)vdesc->vd_offset,
+		       (unsigned long long)vdesc->vd_blocknr,
+		       (unsigned long long)vdesc->vd_vblocknr);
+		brelse(bh);
+		return -EEXIST;
+	}
 	list_add_tail(&bh->b_assoc_buffers, buffers);
 	return 0;
 }
@@ -335,24 +346,10 @@ static int nilfs_ioctl_move_blocks(struct the_nilfs *nilfs,
 	list_for_each_entry_safe(bh, n, &buffers, b_assoc_buffers) {
 		ret = nilfs_gccache_wait_and_mark_dirty(bh);
 		if (unlikely(ret < 0)) {
-			if (ret == -EEXIST) {
-				vdesc = bh->b_private;
-				printk(KERN_CRIT
-				       "%s: conflicting %s buffer: "
-				       "ino=%llu, cno=%llu, offset=%llu, "
-				       "blocknr=%llu, vblocknr=%llu\n",
-				       __func__,
-				       vdesc->vd_flags ? "node" : "data",
-				       (unsigned long long)vdesc->vd_ino,
-				       (unsigned long long)vdesc->vd_cno,
-				       (unsigned long long)vdesc->vd_offset,
-				       (unsigned long long)vdesc->vd_blocknr,
-				       (unsigned long long)vdesc->vd_vblocknr);
-			}
+			WARN_ON(ret == -EEXIST);
 			goto failed;
 		}
 		list_del_init(&bh->b_assoc_buffers);
-		bh->b_private = NULL;
 		brelse(bh);
 	}
 	return nmembs;
@@ -360,7 +357,6 @@ static int nilfs_ioctl_move_blocks(struct the_nilfs *nilfs,
  failed:
 	list_for_each_entry_safe(bh, n, &buffers, b_assoc_buffers) {
 		list_del_init(&bh->b_assoc_buffers);
-		bh->b_private = NULL;
 		brelse(bh);
 	}
 	return ret;