nilfs2: ensure proper cache clearing for gc-inodes

A gc-inode is a pseudo inode used to buffer the blocks to be moved by
garbage collection.

Block caches of gc-inodes must be cleared every time a garbage collection
function (nilfs_clean_segments) completes. Otherwise, stale blocks
buffered in the caches may be wrongly reused in successive calls of the GC
function.

For user files, this is not a problem because their gc-inodes are
distinguished by a checkpoint number as well as an inode number. They
never buffer different blocks if either an inode number, a checkpoint
number, or a block offset differs.

However, gc-inodes of sufile, cpfile and DAT file can store different data
for the same block offset. Thus, the nilfs_clean_segments function can
move incorrect block for these meta-data files if an old block is cached.
I found this is really causing meta-data corruption in nilfs.

This fixes the issue by ensuring cache clear of gc-inodes and resolves
reported GC problems including checkpoint file corruption, b-tree
corruption, and the following warning during GC.

nilfs_palloc_freev: entry number 307234 already freed.
...

Signed-off-by: Ryusuke Konishi <[e-mail]>
Tested-by: Ryusuke Konishi <[e-mail]>
Cc: <[e-mail]> [2.6.37+]
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/nilfs2/gcinode.c

···
 	while (!list_empty(head)) {
 		ii = list_first_entry(head, struct nilfs_inode_info, i_dirty);
 		list_del_init(&ii->i_dirty);
+		truncate_inode_pages(&ii->vfs_inode.i_data, 0);
+		nilfs_btnode_cache_clear(&ii->i_btnode_cache);
 		iput(&ii->vfs_inode);
 	}
 }

fs/nilfs2/segment.c

···
 		if (!test_bit(NILFS_I_UPDATED, &ii->i_state))
 			continue;
 		list_del_init(&ii->i_dirty);
+		truncate_inode_pages(&ii->vfs_inode.i_data, 0);
+		nilfs_btnode_cache_clear(&ii->i_btnode_cache);
 		iput(&ii->vfs_inode);
 	}
 }