btrfs: implement launder_folio for clearing dirty page reserve

In the buffered write path, dirty pages can be said to "own" the qgroup
reservation until they create an ordered_extent. It is possible for
there to be outstanding dirty pages when a transaction is aborted, in
which case there is no cancellation path for freeing this reservation
and it is leaked.

We do already walk the list of outstanding delalloc inodes in
btrfs_destroy_delalloc_inodes() and call invalidate_inode_pages2() on them.

This does *not* call btrfs_invalidate_folio(), as one might guess, but
rather calls launder_folio() and release_folio(). Since this is a
reservation associated with dirty pages only, rather than something
associated with the private bit (ordered_extent is cancelled separately
already in the cleanup transaction path), implementing this release
should be done via launder_folio.
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Boris Burkov <boris@bur.io>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/inode.c

@@ -7202,6 +7202,12 @@ static void wait_subpage_spinlock(struct page *page)
 	spin_unlock_irq(&subpage->lock);
 }
 
+static int btrfs_launder_folio(struct folio *folio)
+{
+	return btrfs_qgroup_free_data(folio_to_inode(folio), NULL, folio_pos(folio),
+				      PAGE_SIZE, NULL);
+}
+
 static bool __btrfs_release_folio(struct folio *folio, gfp_t gfp_flags)
 {
 	if (try_release_extent_mapping(&folio->page, gfp_flags)) {
@@ -10137,6 +10143,7 @@ static const struct address_space_operations btrfs_aops = {
 	.writepages	= btrfs_writepages,
 	.readahead	= btrfs_readahead,
 	.invalidate_folio = btrfs_invalidate_folio,
+	.launder_folio	= btrfs_launder_folio,
 	.release_folio	= btrfs_release_folio,
 	.migrate_folio	= btrfs_migrate_folio,
 	.dirty_folio	= filemap_dirty_folio,