1 files changed, 21 insertions, 7 deletions

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index d7031e7dfd76..7021dde74d81 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -6526,15 +6526,28 @@ static u64 update_block_group_flags(struct btrfs_root *root, u64 flags)
         return flags;
 }
 
-static int set_block_group_ro(struct btrfs_block_group_cache *cache)
+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;
 
         if (cache->ro)
                 return 0;
 
+        /*
+         * 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);
         num_bytes = cache->key.offset - cache->reserved - cache->pinned -
@@ -6542,7 +6555,8 @@ static int set_block_group_ro(struct btrfs_block_group_cache *cache)
 
         if (sinfo->bytes_used + sinfo->bytes_reserved + sinfo->bytes_pinned +
             sinfo->bytes_may_use + sinfo->bytes_readonly +
-            cache->reserved_pinned + num_bytes <= sinfo->total_bytes) {
+            cache->reserved_pinned + num_bytes + min_allocable_bytes <=
+            sinfo->total_bytes) {
                 sinfo->bytes_readonly += num_bytes;
                 sinfo->bytes_reserved += cache->reserved_pinned;
                 cache->reserved_pinned = 0;
@@ -6573,7 +6587,7 @@ int btrfs_set_block_group_ro(struct btrfs_root *root,
                 do_chunk_alloc(trans, root, 2 * 1024 * 1024, alloc_flags,
                                CHUNK_ALLOC_FORCE);
 
-        ret = set_block_group_ro(cache);
+        ret = set_block_group_ro(cache, 0);
         if (!ret)
                 goto out;
         alloc_flags = get_alloc_profile(root, cache->space_info->flags);
@@ -6581,7 +6595,7 @@ int btrfs_set_block_group_ro(struct btrfs_root *root,
                              CHUNK_ALLOC_FORCE);
         if (ret < 0)
                 goto out;
-        ret = set_block_group_ro(cache);
+        ret = set_block_group_ro(cache, 0);
 out:
         btrfs_end_transaction(trans, root);
         return ret;
@@ -7018,7 +7032,7 @@ int btrfs_read_block_groups(struct btrfs_root *root)
 
                 set_avail_alloc_bits(root->fs_info, cache->flags);
                 if (btrfs_chunk_readonly(root, cache->key.objectid))
-                        set_block_group_ro(cache);
+                        set_block_group_ro(cache, 1);
         }
 
         list_for_each_entry_rcu(space_info, &root->fs_info->space_info, list) {
@@ -7032,9 +7046,9 @@ int btrfs_read_block_groups(struct btrfs_root *root)
                  * mirrored block groups.
                  */
                 list_for_each_entry(cache, &space_info->block_groups[3], list)
-                        set_block_group_ro(cache);
+                        set_block_group_ro(cache, 1);
                 list_for_each_entry(cache, &space_info->block_groups[4], list)
-                        set_block_group_ro(cache);
+                        set_block_group_ro(cache, 1);
         }
 
         init_global_block_rsv(info);