btrfs: zoned: unset dedicated block group on allocation failure

Allocating an extent from a block group can fail for various reasons.
When an allocation from a dedicated block group (for tree-log or
relocation data) fails, we need to unregister it as a dedicated one so
that we can allocate a new block group for the dedicated one.

However, we are returning early when the block group in case it is
read-only, fully used, or not be able to activate the zone. As a result,
we keep the non-usable block group as a dedicated one, leading to
further allocation failure. With many block groups, the allocator will
iterate hopeless loop to find a free extent, results in a hung task.

Fix the issue by delaying the return and doing the proper cleanups.

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

fs/btrfs/extent-tree.c

@@ -3805,23 +3805,35 @@ static int do_allocation_zoned(struct btrfs_block_group *block_group,
 	spin_unlock(&fs_info->relocation_bg_lock);
 	if (skip)
 		return 1;
+
 	/* Check RO and no space case before trying to activate it */
 	spin_lock(&block_group->lock);
 	if (block_group->ro ||
 	    block_group->alloc_offset == block_group->zone_capacity) {
-		spin_unlock(&block_group->lock);
-		return 1;
+		ret = 1;
+		/*
+		 * May need to clear fs_info->{treelog,data_reloc}_bg.
+		 * Return the error after taking the locks.
+		 */
 	}
 	spin_unlock(&block_group->lock);
 
-	if (!btrfs_zone_activate(block_group))
-		return 1;
+	if (!ret && !btrfs_zone_activate(block_group)) {
+		ret = 1;
+		/*
+		 * May need to clear fs_info->{treelog,data_reloc}_bg.
+		 * Return the error after taking the locks.
+		 */
+	}
 
 	spin_lock(&space_info->lock);
 	spin_lock(&block_group->lock);
 	spin_lock(&fs_info->treelog_bg_lock);
 	spin_lock(&fs_info->relocation_bg_lock);
 
+	if (ret)
+		goto out;
+
 	ASSERT(!ffe_ctl->for_treelog ||
 	       block_group->start == fs_info->treelog_bg ||
 	       fs_info->treelog_bg == 0);