[PATCH v2 2/2] btrfs: zoned: activate block group only for extent allocation

[Naohiro Aota <naohiro.aota@wdc.com>]

In btrfs_make_block_group(), we activate the allocated block group,
expecting that the block group is soon used for allocation. However, the
chunk allocation from flush_space() context broke the assumption. There can
be a large time gap between the chunk allocation time and the extent
allocation time from the chunk.

Activating the empty block groups pre-allocated from flush_space() context
can exhaust the active zone counter of a device. Once we use all the active
zone counts for empty pre-allocated BGs, we cannot activate new BG for the
other things: metadata, tree-log, or data relocation BG. That failure
results in a fake -ENOSPC.

This patch introduces CHUNK_ALLOC_FORCE_FOR_EXTENT to distinguish the chunk
allocation from find_free_extent(). Now, the new block group is activated
only in that context.

Fixes: eb66a010d518 ("btrfs: zoned: activate new block group")
Cc: stable@vger.kernel.org # 5.16+: c7d1b9109dd0: btrfs: return allocated block group from do_chunk_alloc()
Cc: stable@vger.kernel.org # 5.16+
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
---
 fs/btrfs/block-group.c | 24 ++++++++++++++++--------
 fs/btrfs/block-group.h |  1 +
 fs/btrfs/extent-tree.c |  2 +-
 3 files changed, 18 insertions(+), 9 deletions(-)

diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c
index d4ac1c76f539..84c97d76de92 100644
--- a/fs/btrfs/block-group.c
+++ b/fs/btrfs/block-group.c
@@ -2481,12 +2481,6 @@ struct btrfs_block_group *btrfs_make_block_group(struct btrfs_trans_handle *tran
 		return ERR_PTR(ret);
 	}
 
-	/*
-	 * New block group is likely to be used soon. Try to activate it now.
-	 * Failure is OK for now.
-	 */
-	btrfs_zone_activate(cache);
-
 	ret = exclude_super_stripes(cache);
 	if (ret) {
 		/* We may have excluded something, so call this just in case */
@@ -3642,8 +3636,14 @@ int btrfs_chunk_alloc(struct btrfs_trans_handle *trans, u64 flags,
 	struct btrfs_block_group *ret_bg;
 	bool wait_for_alloc = false;
 	bool should_alloc = false;
+	bool from_extent_allocation = false;
 	int ret = 0;
 
+	if (force == CHUNK_ALLOC_FORCE_FOR_EXTENT) {
+		from_extent_allocation = true;
+		force = CHUNK_ALLOC_FORCE;
+	}
+
 	/* Don't re-enter if we're already allocating a chunk */
 	if (trans->allocating_chunk)
 		return -ENOSPC;
@@ -3736,9 +3736,17 @@ int btrfs_chunk_alloc(struct btrfs_trans_handle *trans, u64 flags,
 	ret_bg = do_chunk_alloc(trans, flags);
 	trans->allocating_chunk = false;
 
-	if (IS_ERR(ret_bg))
+	if (IS_ERR(ret_bg)) {
 		ret = PTR_ERR(ret_bg);
-	else
+	} else if (from_extent_allocation) {
+		/*
+		 * New block group is likely to be used soon. Try to activate
+		 * it now. Failure is OK for now.
+		 */
+		btrfs_zone_activate(ret_bg);
+	}
+
+	if (!ret)
 		btrfs_put_block_group(ret_bg);
 
 	spin_lock(&space_info->lock);
diff --git a/fs/btrfs/block-group.h b/fs/btrfs/block-group.h
index 93aabc68bb6a..9c822367c432 100644
--- a/fs/btrfs/block-group.h
+++ b/fs/btrfs/block-group.h
@@ -40,6 +40,7 @@ enum btrfs_chunk_alloc_enum {
 	CHUNK_ALLOC_NO_FORCE,
 	CHUNK_ALLOC_LIMITED,
 	CHUNK_ALLOC_FORCE,
+	CHUNK_ALLOC_FORCE_FOR_EXTENT,
 };
 
 struct btrfs_caching_control {
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index f477035a2ac2..6aa92f84f465 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -4082,7 +4082,7 @@ static int find_free_extent_update_loop(struct btrfs_fs_info *fs_info,
 			}
 
 			ret = btrfs_chunk_alloc(trans, ffe_ctl->flags,
-						CHUNK_ALLOC_FORCE);
+						CHUNK_ALLOC_FORCE_FOR_EXTENT);
 
 			/* Do not bail out on ENOSPC since we can do more. */
 			if (ret == -ENOSPC)
-- 
2.35.1