nilfs2: fix buffer head leaks in calls to truncate_inode_pages()

When block_invalidatepage was converted to block_invalidate_folio, the
fallback to block_invalidatepage in folio_invalidate() if the
address_space_operations method invalidatepage (currently
invalidate_folio) was not set, was removed.

Unfortunately, some pseudo-inodes in nilfs2 use empty_aops set by
inode_init_always_gfp() as is, or explicitly set it to
address_space_operations.  Therefore, with this change,
block_invalidatepage() is no longer called from folio_invalidate(), and as
a result, the buffer_head structures attached to these pages/folios are no
longer freed via try_to_free_buffers().

Thus, these buffer heads are now leaked by truncate_inode_pages(), which
cleans up the page cache from inode evict(), etc.

Three types of caches use empty_aops: gc inode caches and the DAT shadow
inode used by GC, and b-tree node caches.  Of these, b-tree node caches
explicitly call invalidate_mapping_pages() during cleanup, which involves
calling try_to_free_buffers(), so the leak was not visible during normal
operation but worsened when GC was performed.

Fix this issue by using address_space_operations with invalidate_folio set
to block_invalidate_folio instead of empty_aops, which will ensure the
same behavior as before.

Link: https://lkml.kernel.org/r/20241212164556.21338-1-konishi.ryusuke@gmail.com
Fixes: 7ba13ab ("fs: Turn block_invalidatepage into block_invalidate_folio")
Signed-off-by: Ryusuke Konishi <konishi.ryusuke@gmail.com>
Cc: <stable@vger.kernel.org>	[5.18+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: konis

fs/nilfs2/btnode.c

@@ -35,6 +35,7 @@ void nilfs_init_btnc_inode(struct inode *btnc_inode)
 	ii->i_flags = 0;
 	memset(&ii->i_bmap_data, 0, sizeof(struct nilfs_bmap));
 	mapping_set_gfp_mask(btnc_inode->i_mapping, GFP_NOFS);
+	btnc_inode->i_mapping->a_ops = &nilfs_buffer_cache_aops;
 }
 
 void nilfs_btnode_cache_clear(struct address_space *btnc)

fs/nilfs2/gcinode.c

@@ -163,7 +163,7 @@ int nilfs_init_gcinode(struct inode *inode)
 
 	inode->i_mode = S_IFREG;
 	mapping_set_gfp_mask(inode->i_mapping, GFP_NOFS);
-	inode->i_mapping->a_ops = &empty_aops;
+	inode->i_mapping->a_ops = &nilfs_buffer_cache_aops;
 
 	ii->i_flags = 0;
 	nilfs_bmap_init_gc(ii->i_bmap);

fs/nilfs2/inode.c

@@ -276,6 +276,10 @@ const struct address_space_operations nilfs_aops = {
 	.is_partially_uptodate  = block_is_partially_uptodate,
 };
 
+const struct address_space_operations nilfs_buffer_cache_aops = {
+	.invalidate_folio	= block_invalidate_folio,
+};
+
 static int nilfs_insert_inode_locked(struct inode *inode,
 				     struct nilfs_root *root,
 				     unsigned long ino)
@@ -681,6 +685,7 @@ struct inode *nilfs_iget_for_shadow(struct inode *inode)
 	NILFS_I(s_inode)->i_flags = 0;
 	memset(NILFS_I(s_inode)->i_bmap, 0, sizeof(struct nilfs_bmap));
 	mapping_set_gfp_mask(s_inode->i_mapping, GFP_NOFS);
+	s_inode->i_mapping->a_ops = &nilfs_buffer_cache_aops;
 
 	err = nilfs_attach_btree_node_cache(s_inode);
 	if (unlikely(err)) {

fs/nilfs2/nilfs.h

@@ -401,6 +401,7 @@ extern const struct file_operations nilfs_dir_operations;
 extern const struct inode_operations nilfs_file_inode_operations;
 extern const struct file_operations nilfs_file_operations;
 extern const struct address_space_operations nilfs_aops;
+extern const struct address_space_operations nilfs_buffer_cache_aops;
 extern const struct inode_operations nilfs_dir_inode_operations;
 extern const struct inode_operations nilfs_special_inode_operations;
 extern const struct inode_operations nilfs_symlink_inode_operations;