f2fs: fix to reorder set_page_dirty and wait_on_page_writeback

This patch reorders flow from

- update page
- set_page_dirty
- wait_on_page_writeback

to

- wait_on_page_writeback
- update page
- set_page_dirty

The reason is:
- set_page_dirty will increase reference of dirty page, the reference
should be cleared before wait_on_page_writeback to keep its consistency.
- some devices need stable page during page writebacking, so we
should not change page's data.

Signed-off-by: Chao Yu <[e-mail]>
Signed-off-by: Jaegeuk Kim <[e-mail]>

fs/f2fs/checkpoint.c

···
 	struct page *page = f2fs_grab_meta_page(sbi, blk_addr);
 	int err;
 
-	memcpy(page_address(page), src, PAGE_SIZE);
-	set_page_dirty(page);
-
 	f2fs_wait_on_page_writeback(page, META, true);
 	f2fs_bug_on(sbi, PageWriteback(page));
+
+	memcpy(page_address(page), src, PAGE_SIZE);
+
+	set_page_dirty(page);
 	if (unlikely(!clear_page_dirty_for_io(page)))
 		f2fs_bug_on(sbi, 1);
 

fs/f2fs/gc.c

···
 	}
 
 write_page:
-	set_page_dirty(fio.encrypted_page);
 	f2fs_wait_on_page_writeback(fio.encrypted_page, DATA, true);
+	set_page_dirty(fio.encrypted_page);
 	if (clear_page_dirty_for_io(fio.encrypted_page))
 		dec_page_count(fio.sbi, F2FS_DIRTY_META);
 
···
 		bool is_dirty = PageDirty(page);
 
 retry:
-		set_page_dirty(page);
 		f2fs_wait_on_page_writeback(page, DATA, true);
+
+		set_page_dirty(page);
 		if (clear_page_dirty_for_io(page)) {
 			inode_dec_dirty_pages(inode);
 			f2fs_remove_dirty_inode(inode);

fs/f2fs/node.c

···
 			.for_reclaim = 0,
 		};
 
-		set_page_dirty(node_page);
 		f2fs_wait_on_page_writeback(node_page, NODE, true);
-
 		f2fs_bug_on(F2FS_P_SB(node_page), PageWriteback(node_page));
+
+		set_page_dirty(node_page);
+
 		if (!clear_page_dirty_for_io(node_page)) {
 			err = -EAGAIN;
 			goto out_page;

fs/f2fs/segment.c

···
 		if (page->mapping == inode->i_mapping) {
 			trace_f2fs_commit_inmem_page(page, INMEM);
 
-			set_page_dirty(page);
 			f2fs_wait_on_page_writeback(page, DATA, true);
+
+			set_page_dirty(page);
 			if (clear_page_dirty_for_io(page)) {
 				inode_dec_dirty_pages(inode);
 				f2fs_remove_dirty_inode(inode);