From ea08eeccae9297f7aabd2ef7f0c2517ac4549acc Mon Sep 17 00:00:00 2001
From: hc <hc@nodka.com>
Date: Tue, 20 Feb 2024 01:18:26 +0000
Subject: [PATCH] write in 30M

---
 kernel/fs/btrfs/qgroup.c |   57 +++++++++++++++++++++++++++++++++++++++++++++------------
 1 files changed, 45 insertions(+), 12 deletions(-)

diff --git a/kernel/fs/btrfs/qgroup.c b/kernel/fs/btrfs/qgroup.c
index 74cbbb5..a67323c 100644
--- a/kernel/fs/btrfs/qgroup.c
+++ b/kernel/fs/btrfs/qgroup.c
@@ -1202,11 +1202,22 @@
 	int ret = 0;
 
 	/*
-	 * We need to have subvol_sem write locked, to prevent races between
-	 * concurrent tasks trying to disable quotas, because we will unlock
-	 * and relock qgroup_ioctl_lock across BTRFS_FS_QUOTA_ENABLED changes.
+	 * We need to have subvol_sem write locked to prevent races with
+	 * snapshot creation.
 	 */
 	lockdep_assert_held_write(&fs_info->subvol_sem);
+
+	/*
+	 * Lock the cleaner mutex to prevent races with concurrent relocation,
+	 * because relocation may be building backrefs for blocks of the quota
+	 * root while we are deleting the root. This is like dropping fs roots
+	 * of deleted snapshots/subvolumes, we need the same protection.
+	 *
+	 * This also prevents races between concurrent tasks trying to disable
+	 * quotas, because we will unlock and relock qgroup_ioctl_lock across
+	 * BTRFS_FS_QUOTA_ENABLED changes.
+	 */
+	mutex_lock(&fs_info->cleaner_mutex);
 
 	mutex_lock(&fs_info->qgroup_ioctl_lock);
 	if (!fs_info->quota_root)
@@ -1270,7 +1281,9 @@
 		goto out;
 	}
 
+	spin_lock(&fs_info->trans_lock);
 	list_del(&quota_root->dirty_list);
+	spin_unlock(&fs_info->trans_lock);
 
 	btrfs_tree_lock(quota_root->node);
 	btrfs_clean_tree_block(quota_root->node);
@@ -1285,6 +1298,7 @@
 		btrfs_end_transaction(trans);
 	else if (trans)
 		ret = btrfs_end_transaction(trans);
+	mutex_unlock(&fs_info->cleaner_mutex);
 
 	return ret;
 }
@@ -2762,12 +2776,21 @@
 }
 
 /*
- * called from commit_transaction. Writes all changed qgroups to disk.
+ * Writes all changed qgroups to disk.
+ * Called by the transaction commit path and the qgroup assign ioctl.
  */
 int btrfs_run_qgroups(struct btrfs_trans_handle *trans)
 {
 	struct btrfs_fs_info *fs_info = trans->fs_info;
 	int ret = 0;
+
+	/*
+	 * In case we are called from the qgroup assign ioctl, assert that we
+	 * are holding the qgroup_ioctl_lock, otherwise we can race with a quota
+	 * disable operation (ioctl) and access a freed quota root.
+	 */
+	if (trans->transaction->state != TRANS_STATE_COMMIT_DOING)
+		lockdep_assert_held(&fs_info->qgroup_ioctl_lock);
 
 	if (!fs_info->quota_root)
 		return ret;
@@ -3296,6 +3319,7 @@
 	int err = -ENOMEM;
 	int ret = 0;
 	bool stopped = false;
+	bool did_leaf_rescans = false;
 
 	path = btrfs_alloc_path();
 	if (!path)
@@ -3316,6 +3340,7 @@
 		}
 
 		err = qgroup_rescan_leaf(trans, path);
+		did_leaf_rescans = true;
 
 		if (err > 0)
 			btrfs_commit_transaction(trans);
@@ -3336,16 +3361,23 @@
 	mutex_unlock(&fs_info->qgroup_rescan_lock);
 
 	/*
-	 * only update status, since the previous part has already updated the
-	 * qgroup info.
+	 * Only update status, since the previous part has already updated the
+	 * qgroup info, and only if we did any actual work. This also prevents
+	 * race with a concurrent quota disable, which has already set
+	 * fs_info->quota_root to NULL and cleared BTRFS_FS_QUOTA_ENABLED at
+	 * btrfs_quota_disable().
 	 */
-	trans = btrfs_start_transaction(fs_info->quota_root, 1);
-	if (IS_ERR(trans)) {
-		err = PTR_ERR(trans);
+	if (did_leaf_rescans) {
+		trans = btrfs_start_transaction(fs_info->quota_root, 1);
+		if (IS_ERR(trans)) {
+			err = PTR_ERR(trans);
+			trans = NULL;
+			btrfs_err(fs_info,
+				  "fail to start transaction for status update: %d",
+				  err);
+		}
+	} else {
 		trans = NULL;
-		btrfs_err(fs_info,
-			  "fail to start transaction for status update: %d",
-			  err);
 	}
 
 	mutex_lock(&fs_info->qgroup_rescan_lock);
@@ -4356,4 +4388,5 @@
 		ulist_free(entry->old_roots);
 		kfree(entry);
 	}
+	*root = RB_ROOT;
 }

--
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