[PATCH] btrfs: delete chunk allocation attemp when setting block group ro

[Shaohua Li <shli@xxxxxx>]

Below test will fail currently:
  mkfs.ext4 -F /dev/sda
  btrfs-convert /dev/sda
  mount /dev/sda /mnt
  btrfs device add -f /dev/sdb /mnt
  btrfs balance start -v -dconvert=raid1 -mconvert=raid1 /mnt

The reason is there are some block groups with usage 0, but the whole
disk hasn't free space to allocate new chunk, so we even can't set such
block group readonly. This patch deletes the chunk allocation when
setting block group ro. For META, we already have reserve. But for
SYSTEM, we don't have, so the check_system_chunk is still required.

Signed-off-by: Shaohua Li <shli@xxxxxx>
---
 fs/btrfs/extent-tree.c | 31 +++++++------------------------
 1 file changed, 7 insertions(+), 24 deletions(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index a80b971..430101b6 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -8493,22 +8493,8 @@ static int set_block_group_ro(struct btrfs_block_group_cache *cache, int force)
 {
 	struct btrfs_space_info *sinfo = cache->space_info;
 	u64 num_bytes;
-	u64 min_allocable_bytes;
 	int ret = -ENOSPC;
 
-
-	/*
-	 * We need some metadata space and system metadata space for
-	 * allocating chunks in some corner cases until we force to set
-	 * it to be readonly.
-	 */
-	if ((sinfo->flags &
-	     (BTRFS_BLOCK_GROUP_SYSTEM | BTRFS_BLOCK_GROUP_METADATA)) &&
-	    !force)
-		min_allocable_bytes = 1 * 1024 * 1024;
-	else
-		min_allocable_bytes = 0;
-
 	spin_lock(&sinfo->lock);
 	spin_lock(&cache->lock);
 
@@ -8521,8 +8507,8 @@ static int set_block_group_ro(struct btrfs_block_group_cache *cache, int force)
 		    cache->bytes_super - btrfs_block_group_used(&cache->item);
 
 	if (sinfo->bytes_used + sinfo->bytes_reserved + sinfo->bytes_pinned +
-	    sinfo->bytes_may_use + sinfo->bytes_readonly + num_bytes +
-	    min_allocable_bytes <= sinfo->total_bytes) {
+	    sinfo->bytes_may_use + sinfo->bytes_readonly + num_bytes
+	    <= sinfo->total_bytes) {
 		sinfo->bytes_readonly += num_bytes;
 		cache->ro = 1;
 		list_add_tail(&cache->ro_list, &sinfo->ro_bgs);
@@ -8548,14 +8534,6 @@ int btrfs_set_block_group_ro(struct btrfs_root *root,
 	if (IS_ERR(trans))
 		return PTR_ERR(trans);
 
-	alloc_flags = update_block_group_flags(root, cache->flags);
-	if (alloc_flags != cache->flags) {
-		ret = do_chunk_alloc(trans, root, alloc_flags,
-				     CHUNK_ALLOC_FORCE);
-		if (ret < 0)
-			goto out;
-	}
-
 	ret = set_block_group_ro(cache, 0);
 	if (!ret)
 		goto out;
@@ -8566,6 +8544,11 @@ int btrfs_set_block_group_ro(struct btrfs_root *root,
 		goto out;
 	ret = set_block_group_ro(cache, 0);
 out:
+	if (cache->flags & BTRFS_BLOCK_GROUP_SYSTEM) {
+		alloc_flags = update_block_group_flags(root, cache->flags);
+		check_system_chunk(trans, root, alloc_flags);
+	}
+
 	btrfs_end_transaction(trans, root);
 	return ret;
 }
-- 
1.8.1

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