btrfs: zoned: fix chunk allocation condition for zoned allocator

The ZNS specification defines a limit on the number of "active"
zones. That limit impose us to limit the number of block groups which
can be used for an allocation at the same time. Not to exceed the
limit, we reuse the existing active block groups as much as possible
when we can't activate any other zones without sacrificing an already
activated block group in commit a85f05e59bc1 ("btrfs: zoned: avoid
chunk allocation if active block group has enough space").

However, the check is wrong in two ways. First, it checks the
condition for every raid index (ffe_ctl->index). Even if it reaches
the condition and "ffe_ctl->max_extent_size >=
ffe_ctl->min_alloc_size" is met, there can be other block groups
having enough space to hold ffe_ctl->num_bytes. (Actually, this won't
happen in the current zoned code as it only supports SINGLE
profile. But, it can happen once it enables other RAID types.)

Second, it checks the active zone availability depending on the
raid index. The raid index is just an index for
space_info->block_groups, so it has nothing to do with chunk allocation.

These mistakes are causing a faulty allocation in a certain
situation. Consider we are running zoned btrfs on a device whose
max_active_zone == 0 (no limit). And, suppose no block group have a
room to fit ffe_ctl->num_bytes but some room to meet
ffe_ctl->min_alloc_size (i.e. max_extent_size > num_bytes >=
min_alloc_size).

In this situation, the following occur:

- With SINGLE raid_index, it reaches the chunk allocation checking
  code
- The check returns true because we can activate a new zone (no limit)
- But, before allocating the chunk, it iterates to the next raid index
  (RAID5)
- Since there are no RAID5 block groups on zoned mode, it again
  reaches the check code
- The check returns false because of btrfs_can_activate_zone()'s "if
  (raid_index != BTRFS_RAID_SINGLE)" part
- That results in returning -ENOSPC without allocating a new chunk

As a result, we end up hitting -ENOSPC too early.

Move the check to the right place in the can_allocate_chunk() hook,
and do the active zone check depending on the allocation flag, not on
the raid index.

CC: stable@vger.kernel.org # 5.16
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 2 insertions, 3 deletions

diff --git a/fs/btrfs/zoned.h b/fs/btrfs/zoned.h
index a7b4cd6dd9f4..cbf016a7bb5d 100644
--- a/fs/btrfs/zoned.h
+++ b/fs/btrfs/zoned.h
@@ -73,8 +73,7 @@ struct btrfs_device *btrfs_zoned_get_device(struct btrfs_fs_info *fs_info,
 					    u64 logical, u64 length);
 bool btrfs_zone_activate(struct btrfs_block_group *block_group);
 int btrfs_zone_finish(struct btrfs_block_group *block_group);
-bool btrfs_can_activate_zone(struct btrfs_fs_devices *fs_devices,
-			     int raid_index);
+bool btrfs_can_activate_zone(struct btrfs_fs_devices *fs_devices, u64 flags);
 void btrfs_zone_finish_endio(struct btrfs_fs_info *fs_info, u64 logical,
 			     u64 length);
 void btrfs_clear_data_reloc_bg(struct btrfs_block_group *bg);
@@ -226,7 +225,7 @@ static inline int btrfs_zone_finish(struct btrfs_block_group *block_group)
 }
 
 static inline bool btrfs_can_activate_zone(struct btrfs_fs_devices *fs_devices,
-					   int raid_index)
+					   u64 flags)
 {
 	return true;
 }