f2fs: fix to clear FI_VOLATILE_FILE correctly

From: Chao Yu <[email protected]>

Thread A Thread B
- f2fs_release_file
- clear_inode_flag(FI_VOLATILE_FILE)
- wb_writeback
- writeback_sb_inodes
- __writeback_single_inode
- do_writepages
- f2fs_write_data_pages
- __write_data_page all volatile file's pages are writebacked to storage
- set_inode_flag(FI_DROP_CACHE)
- filemap_fdatawrite

There is a hole that mm can flush all dirty pages of volatile file as inode is not tagged with both FI_VOLATILE_FILE and FI_DROP_CACHE flags, we should never writeback the page #0 and also it's unneeded to writeback other pages.

This patch adjusts to relocate clear_inode_flag(FI_VOLATILE_FILE), so that FI_VOLATILE_FILE flag can be remained before all dirty pages were dropped to avoid issue.

---
 fs/f2fs/file.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

index 16fd50abbf40..13f2f6845e87 100644
@@ -1564,11 +1564,11 @@ static int f2fs_release_file(struct inode *inode, struct file *filp)
 	if (f2fs_is_atomic_file(inode))
 		f2fs_drop_inmem_pages(inode);
 	if (f2fs_is_volatile_file(inode)) {
-		clear_inode_flag(inode, FI_VOLATILE_FILE);
-		stat_dec_volatile_write(inode);
 		set_inode_flag(inode, FI_DROP_CACHE);
 		filemap_fdatawrite(inode->i_mapping);
 		clear_inode_flag(inode, FI_DROP_CACHE);
+		clear_inode_flag(inode, FI_VOLATILE_FILE);
+		stat_dec_volatile_write(inode);
 	}
 	return 0;
 }

2.16.2.17.g38e79b1fd