Re: [PATCH v5 15/18] btrfs: check generation when recording simple quota delta

David Sterba
2023-09-07T17:25:56Z

On Thu, Jul 27, 2023 at 03:13:02PM -0700, Boris Burkov wrote:
> Simple quotas count extents only from the moment the feature is enabled.
> Therefore, if we do something like:
> 1. create subvol S
> 2. write F in S
> 3. enable quotas
> 4. remove F
> 5. write G in S
>
> then after 3. and 4. we would expect the simple quota usage of S to be 0
> (putting aside some metadata extents that might be written) and after
> 5., it should be the size of G plus metadata. Therefore, we need to be
> able to determine whether a particular quota delta we are processing
> predates simple quota enablement.
>
> To do this, store the transaction id when quotas were enabled. In
> fs_info for immediate use and in the quota status item to make it
> recoverable on mount. When we see a delta, check if the generation of
> the extent item is less than that of quota enablement. If so, we should
> ignore the delta from this extent.
>
> Signed-off-by: Boris Burkov <boris@bur.io>
> ---
> fs/btrfs/accessors.h | 2 ++
> fs/btrfs/extent-tree.c | 4 ++++
> fs/btrfs/fs.h | 2 ++
> fs/btrfs/qgroup.c | 14 ++++++++++++--
> fs/btrfs/qgroup.h | 1 +
> include/uapi/linux/btrfs_tree.h | 7 +++++++
> 6 files changed, 28 insertions(+), 2 deletions(-)
>
> diff --git a/fs/btrfs/accessors.h b/fs/btrfs/accessors.h
> index a23045c05937..513f8edbd98e 100644
> --- a/fs/btrfs/accessors.h
> +++ b/fs/btrfs/accessors.h
> @@ -970,6 +970,8 @@ BTRFS_SETGET_FUNCS(qgroup_status_flags, struct btrfs_qgroup_status_item,
> flags, 64);
> BTRFS_SETGET_FUNCS(qgroup_status_rescan, struct btrfs_qgroup_status_item,
> rescan, 64);
> +BTRFS_SETGET_FUNCS(qgroup_status_enable_gen, struct btrfs_qgroup_status_item,
> + enable_gen, 64);
>
> /* btrfs_qgroup_info_item */
> BTRFS_SETGET_FUNCS(qgroup_info_generation, struct btrfs_qgroup_info_item,
> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
> index 1b5efd03ef83..395ab46e520b 100644
> --- a/fs/btrfs/extent-tree.c
> +++ b/fs/btrfs/extent-tree.c
> @@ -1513,6 +1513,7 @@ static int run_delayed_data_ref(struct btrfs_trans_handle *trans,
> .rsv_bytes = href->reserved_bytes,
> .is_data = true,
> .is_inc = true,
> + .generation = trans->transid,
> };
>
> if (extent_op)
> @@ -1676,6 +1677,7 @@ static int run_delayed_tree_ref(struct btrfs_trans_handle *trans,
> .rsv_bytes = 0,
> .is_data = false,
> .is_inc = true,
> + .generation = trans->transid,
> };
>
> BUG_ON(!extent_op || !extent_op->update_flags);
> @@ -3217,6 +3219,7 @@ static int __btrfs_free_extent(struct btrfs_trans_handle *trans,
> .rsv_bytes = 0,
> .is_data = is_data,
> .is_inc = false,
> + .generation = btrfs_extent_generation(leaf, ei),
> };
>
> /* In this branch refs == 1 */
> @@ -4850,6 +4853,7 @@ int btrfs_alloc_logged_file_extent(struct btrfs_trans_handle *trans,
> struct btrfs_simple_quota_delta delta = {
> .root = root_objectid,
> .num_bytes = ins->offset,
> + .generation = trans->transid,
> .rsv_bytes = 0,
> .is_data = true,
> .is_inc = true,
> diff --git a/fs/btrfs/fs.h b/fs/btrfs/fs.h
> index f76f450c2abf..da7b623ff15f 100644
> --- a/fs/btrfs/fs.h
> +++ b/fs/btrfs/fs.h
> @@ -802,6 +802,8 @@ struct btrfs_fs_info {
> spinlock_t eb_leak_lock;
> struct list_head allocated_ebs;
> #endif
> +
> + u64 quota_enable_gen;

Please move it to the other quota/qgroup related members, at the end of
fs_info there's only debugging stuff.

> };
>
> static inline void btrfs_set_last_root_drop_gen(struct btrfs_fs_info *fs_info,
> diff --git a/fs/btrfs/qgroup.c b/fs/btrfs/qgroup.c
> index 58e9ed0deedd..a8a603242431 100644
> --- a/fs/btrfs/qgroup.c
> +++ b/fs/btrfs/qgroup.c
> @@ -454,6 +454,8 @@ int btrfs_read_qgroup_config(struct btrfs_fs_info *fs_info)
> }
> fs_info->qgroup_flags = btrfs_qgroup_status_flags(l, ptr);
> simple = fs_info->qgroup_flags & BTRFS_QGROUP_STATUS_FLAG_SIMPLE;
> + if (simple)
> + fs_info->quota_enable_gen = btrfs_qgroup_status_enable_gen(l, ptr);
> if (btrfs_qgroup_status_generation(l, ptr) !=
> fs_info->generation && !simple) {
> qgroup_mark_inconsistent(fs_info);
> @@ -1107,10 +1109,12 @@ int btrfs_quota_enable(struct btrfs_fs_info *fs_info,
> btrfs_set_qgroup_status_generation(leaf, ptr, trans->transid);
> btrfs_set_qgroup_status_version(leaf, ptr, BTRFS_QGROUP_STATUS_VERSION);
> fs_info->qgroup_flags = BTRFS_QGROUP_STATUS_FLAG_ON;
> - if (simple)
> + if (simple) {
> fs_info->qgroup_flags |= BTRFS_QGROUP_STATUS_FLAG_SIMPLE;
> - else
> + btrfs_set_qgroup_status_enable_gen(leaf, ptr, trans->transid);
> + } else {
> fs_info->qgroup_flags |= BTRFS_QGROUP_STATUS_FLAG_INCONSISTENT;
> + }
> btrfs_set_qgroup_status_flags(leaf, ptr, fs_info->qgroup_flags &
> BTRFS_QGROUP_STATUS_FLAGS_MASK);
> btrfs_set_qgroup_status_rescan(leaf, ptr, 0);
> @@ -1202,6 +1206,8 @@ int btrfs_quota_enable(struct btrfs_fs_info *fs_info,
> goto out_free_path;
> }
>
> + fs_info->quota_enable_gen = trans->transid;
> +
> mutex_unlock(&fs_info->qgroup_ioctl_lock);
> /*
> * Commit the transaction while not holding qgroup_ioctl_lock, to avoid
> @@ -4622,6 +4628,10 @@ int btrfs_record_simple_quota_delta(struct btrfs_fs_info *fs_info,
> if (!is_fstree(root))
> return 0;
>
> + /* If the extent predates enabling quotas, don't count it. */
> + if (delta->generation < fs_info->quota_enable_gen)
> + return 0;
> +
> spin_lock(&fs_info->qgroup_lock);
> qgroup = find_qgroup_rb(fs_info, root);
> if (!qgroup) {
> diff --git a/fs/btrfs/qgroup.h b/fs/btrfs/qgroup.h
> index ce6fa8694ca7..ae1ce14b365c 100644
> --- a/fs/btrfs/qgroup.h
> +++ b/fs/btrfs/qgroup.h
> @@ -241,6 +241,7 @@ struct btrfs_simple_quota_delta {
> u64 rsv_bytes; /* The number of bytes reserved for this extent */
> bool is_inc; /* Whether we are using or freeing the extent */
> bool is_data; /* Whether the extent is data or metadata */
> + u64 generation; /* The generation the extent was created in */

Please reorder it so it does not leave gaps between struct members.

> };
>
> static inline u64 btrfs_qgroup_subvolid(u64 qgroupid)
> diff --git a/include/uapi/linux/btrfs_tree.h b/include/uapi/linux/btrfs_tree.h
> index eacb26caf3c6..1120ce3dae42 100644
> --- a/include/uapi/linux/btrfs_tree.h
> +++ b/include/uapi/linux/btrfs_tree.h
> @@ -1242,6 +1242,13 @@ struct btrfs_qgroup_status_item {
> * of the scan. It contains a logical address
> */
> __le64 rescan;
> +
> + /*
> + * the generation when quotas are enabled. Used by simple quotas to
> + * avoid decrementing when freeing an extent that was written before
> + * enable.
> + */
> + __le64 enable_gen;

This is public interface and btrfs_qgroup_status_item is used in many
places in user space at least in btrfs-progs. This needs a lot of
sanity checks.

> } __attribute__ ((__packed__));
>
> struct btrfs_qgroup_info_item {
> --
> 2.41.0