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

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 <redacted>
---
 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;

 };
 
 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 */

 };
 
 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;