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2024-02-20 102a0743326a03cd1a1202ceda21e175b7d3575c

 kernel/fs/btrfs/volumes.c
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@@ -381,6 +381,7 @@
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 static void free_fs_devices(struct btrfs_fs_devices *fs_devices)
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 {
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 	struct btrfs_device *device;
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+
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 	WARN_ON(fs_devices->opened);
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 	while (!list_empty(&fs_devices->devices)) {
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 		device = list_entry(fs_devices->devices.next,
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@@ -715,6 +716,14 @@
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 	blkdev_put(bdev, flags);
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 	return -EINVAL;
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+}
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+
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+u8 *btrfs_sb_fsid_ptr(struct btrfs_super_block *sb)
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+{
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+	bool has_metadata_uuid = (btrfs_super_incompat_flags(sb) &
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+				  BTRFS_FEATURE_INCOMPAT_METADATA_UUID);
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+
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+	return has_metadata_uuid ? sb->metadata_uuid : sb->fsid;
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 }
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 /*
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@@ -1227,8 +1236,21 @@
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 	mutex_lock(&uuid_mutex);
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 	close_fs_devices(fs_devices);
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-	if (!fs_devices->opened)
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+	if (!fs_devices->opened) {
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 		list_splice_init(&fs_devices->seed_list, &list);
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+
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+		/*
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+		 * If the struct btrfs_fs_devices is not assembled with any
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+		 * other device, it can be re-initialized during the next mount
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+		 * without the needing device-scan step. Therefore, it can be
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+		 * fully freed.
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+		 */
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+		if (fs_devices->num_devices == 1) {
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+			list_del(&fs_devices->fs_list);
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+			free_fs_devices(fs_devices);
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+		}
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+	}
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+
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 	list_for_each_entry_safe(fs_devices, tmp, &list, seed_list) {
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 		close_fs_devices(fs_devices);
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@@ -1396,8 +1418,17 @@
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 	 * later supers, using BTRFS_SUPER_MIRROR_MAX instead
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 	 */
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 	bytenr = btrfs_sb_offset(0);
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-	flags |= FMODE_EXCL;
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+	/*
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+	 * Avoid using flag |= FMODE_EXCL here, as the systemd-udev may
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+	 * initiate the device scan which may race with the user's mount
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+	 * or mkfs command, resulting in failure.
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+	 * Since the device scan is solely for reading purposes, there is
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+	 * no need for FMODE_EXCL. Additionally, the devices are read again
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+	 * during the mount process. It is ok to get some inconsistent
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+	 * values temporarily, as the device paths of the fsid are the only
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+	 * required information for assembling the volume.
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+	 */
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 	bdev = blkdev_get_by_path(path, flags, holder);
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 	if (IS_ERR(bdev))
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 		return ERR_CAST(bdev);
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@@ -1579,7 +1610,7 @@
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 			goto out;
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 	}
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-	while (1) {
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+	while (search_start < search_end) {
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 		l = path->nodes[0];
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 		slot = path->slots[0];
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 		if (slot >= btrfs_header_nritems(l)) {
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@@ -1601,6 +1632,9 @@
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 		if (key.type != BTRFS_DEV_EXTENT_KEY)
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 			goto next;
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+
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+		if (key.offset > search_end)
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+			break;
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 		if (key.offset > search_start) {
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 			hole_size = key.offset - search_start;
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@@ -1662,6 +1696,7 @@
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 	else
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 		ret = 0;
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+	ASSERT(max_hole_start + max_hole_size <= search_end);
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 out:
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 	btrfs_free_path(path);
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 	*start = max_hole_start;
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@@ -4432,8 +4467,7 @@
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 		}
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 	}
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-	BUG_ON(fs_info->balance_ctl ||
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-		test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags));
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+	ASSERT(!test_bit(BTRFS_FS_BALANCE_RUNNING, &fs_info->flags));
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 	atomic_dec(&fs_info->balance_cancel_req);
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 	mutex_unlock(&fs_info->balance_mutex);
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 	return 0;