From: Qu Wenruo <quwenruo.btrfs@gmx.com>
To: Boris Burkov <boris@bur.io>,
linux-btrfs@vger.kernel.org, kernel-team@fb.com
Subject: Re: [PATCH] btrfs: fix qgroup id collision across mounts
Date: Fri, 10 May 2024 08:43:00 +0930 [thread overview]
Message-ID: <5c88c882-d153-453a-88d4-4fd16c090ed3@gmx.com> (raw)
In-Reply-To: <f7e7c99aded1f18703dd19ec6b92cf3c7d635060.1715296042.git.boris@bur.io>
在 2024/5/10 08:37, Boris Burkov 写道:
> If we delete subvolumes whose ID is the largest in the filesystem, then
> unmount and mount again, then btrfs_init_root_free_objectid on the
> tree_root will select a subvolid smaller than that one and thus allow
> reusing it.
>
> If we are also using qgroups (and particularly squotas) it is possible
> to delete the subvol without deleting the qgroup. In that case, we will
> be able to create a new subvol whose id already has a level 0 qgroup.
> This will result in re-using that qgroup which would then lead to
> incorrect accounting.
>
> Fixes: 6ed05643ddb1 ("btrfs: create qgroup earlier in snapshot creation")
> Signed-off-by: Boris Burkov <boris@bur.io>
Reviewed-by: Qu Wenruo <wqu@suse.com>
This also affects regular qgroup, e.g. the qgroup is already
inconsistent, then the delete subvolume would leave a non-empty qgroup.
Although it's less severe, since we need a rescan anyway.
But for squota it's really severe since there is no inconsistent status
at all.
Thanks,
Qu
> ---
> fs/btrfs/qgroup.c | 20 ++++++++++++++++++++
> 1 file changed, 20 insertions(+)
>
> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
> index 2cba6451d164..243995b95e63 100644
> --- a/fs/btrfs/qgroup.c
> +++ b/fs/btrfs/qgroup.c
> @@ -468,6 +468,7 @@ int btrfs_read_qgroup_config(struct btrfs_fs_info *fs_info)
> }
> if (!qgroup) {
> struct btrfs_qgroup *prealloc;
> + struct btrfs_root *tree_root = fs_info->tree_root;
>
> prealloc = kzalloc(sizeof(*prealloc), GFP_KERNEL);
> if (!prealloc) {
> @@ -475,6 +476,25 @@ int btrfs_read_qgroup_config(struct btrfs_fs_info *fs_info)
> goto out;
> }
> qgroup = add_qgroup_rb(fs_info, prealloc, found_key.offset);
> + /*
> + * If a qgroup exists for a subvolume ID, it is possible
> + * that subvolume has been deleted, in which case
> + * re-using that ID would lead to incorrect accounting.
> + *
> + * Ensure that we skip any such subvol ids.
> + *
> + * We don't need to lock because this is only called
> + * during mount before we start doing things like creating
> + * subvolumes.
> + */
> + if (is_fstree(qgroup->qgroupid) &&
> + qgroup->qgroupid > tree_root->free_objectid)
> + /*
> + * Don't need to check against BTRFS_LAST_FREE_OBJECTID,
> + * as it will get checked on the next call to
> + * btrfs_get_free_objectid.
> + */
> + tree_root->free_objectid = qgroup->qgroupid + 1;
> }
> ret = btrfs_sysfs_add_one_qgroup(fs_info, qgroup);
> if (ret < 0)
prev parent reply other threads:[~2024-05-09 23:13 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-05-09 23:07 [PATCH] btrfs: fix qgroup id collision across mounts Boris Burkov
2024-05-09 23:13 ` Qu Wenruo [this message]
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