FAILED: patch "[PATCH] btrfs: qgroup: Fix reserved data space leak if we have" failed to apply to 4.9-stable tree

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From d4e204948fe3e0dc8e1fbf3f8f3290c9c2823be3 Mon Sep 17 00:00:00 2001
From: Qu Wenruo <[email protected]>
Date: Mon, 16 Sep 2019 20:02:39 +0800
Subject: [PATCH] btrfs: qgroup: Fix reserved data space leak if we have
multiple reserve calls

[BUG]
The following script can cause btrfs qgroup data space leak:

mkfs.btrfs -f $dev
mount $dev -o nospace_cache $mnt

btrfs subv create $mnt/subv
btrfs quota en $mnt
btrfs quota rescan -w $mnt
btrfs qgroup limit 128m $mnt/subv

for (( i = 0; i < 3; i++)); do
# Create 3 64M holes for latter fallocate to fail truncate -s 192m $mnt/subv/file
xfs_io -c "pwrite 64m 4k" $mnt/subv/file > /dev/null xfs_io -c "pwrite 128m 4k" $mnt/subv/file > /dev/null sync

# it's supposed to fail, and each failure will leak at least 64M # data space
xfs_io -f -c "falloc 0 192m" $mnt/subv/file &> /dev/null rm $mnt/subv/file
sync
done

# Shouldn't fail after we removed the file
xfs_io -f -c "falloc 0 64m" $mnt/subv/file

[CAUSE]
Btrfs qgroup data reserve code allow multiple reservations to happen on a single extent_changeset:
E.g:

	btrfs_qgroup_reserve_data(inode, &data_reserved, 0, SZ_1M);
	btrfs_qgroup_reserve_data(inode, &data_reserved, SZ_1M, SZ_2M);
	btrfs_qgroup_reserve_data(inode, &data_reserved, 0, SZ_4M);

Btrfs qgroup code has its internal tracking to make sure we don't double-reserve in above example.

The only pattern utilizing this feature is in the main while loop of btrfs_fallocate() function.

However btrfs_qgroup_reserve_data()'s error handling has a bug in that on error it clears all ranges in the io_tree with EXTENT_QGROUP_RESERVED flag but doesn't free previously reserved bytes.

This bug has a two fold effect:
- Clearing EXTENT_QGROUP_RESERVED ranges
This is the correct behavior, but it prevents btrfs_qgroup_check_reserved_leak() to catch the leakage as the detector is purely EXTENT_QGROUP_RESERVED flag based.

- Leak the previously reserved data bytes.

The bug manifests when N calls to btrfs_qgroup_reserve_data are made and the last one fails, leaking space reserved in the previous ones.

[FIX]
Also free previously reserved data bytes when btrfs_qgroup_reserve_data fails.

index 4ab85555a947..c4bb69941c77 100644
@@ -3442,6 +3442,9 @@ int btrfs_qgroup_reserve_data(struct inode *inode,
 	while ((unode = ulist_next(&reserved->range_changed, &uiter)))
 		clear_extent_bit(&BTRFS_I(inode)->io_tree, unode->val,
 				 unode->aux, EXTENT_QGROUP_RESERVED, 0, 0, NULL);
+	/* Also free data bytes of already reserved one */
+	btrfs_qgroup_free_refroot(root->fs_info, root->root_key.objectid,
+				  orig_reserved, BTRFS_QGROUP_RSV_DATA);
 	extent_changeset_release(reserved);
 	return ret;
 }