f2fs: remain written times to update inode during fsync

This fixes xfstests/generic/392.

The failure was caused by different times between 1) one marked in the last
fsync(2) call and 2) the other given by roll-forward recovery after power-cut.
The reason was that we skipped updating inode block at 1), since its i_size
was recoverable along with 4KB-aligned data writes, which was fixed by:
  "f2fs: fix a wrong condition in f2fs_skip_inode_update"

Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/f2fs.h

@@ -664,6 +664,7 @@ struct f2fs_inode_info {
 	kprojid_t i_projid;		/* id for project quota */
 	int i_inline_xattr_size;	/* inline xattr size */
 	struct timespec i_crtime;	/* inode creation time */
+	struct timespec i_disk_time[4];	/* inode disk times */
 };
 
 static inline void get_extent_info(struct extent_info *ext,
@@ -2474,6 +2475,16 @@ static inline bool f2fs_skip_inode_update(struct inode *inode, int dsync)
 			i_size_read(inode) & ~PAGE_MASK)
 		return false;
 
+	if (!timespec_equal(F2FS_I(inode)->i_disk_time, &inode->i_atime))
+		return false;
+	if (!timespec_equal(F2FS_I(inode)->i_disk_time + 1, &inode->i_ctime))
+		return false;
+	if (!timespec_equal(F2FS_I(inode)->i_disk_time + 2, &inode->i_mtime))
+		return false;
+	if (!timespec_equal(F2FS_I(inode)->i_disk_time + 3,
+						&F2FS_I(inode)->i_crtime))
+		return false;
+
 	down_read(&F2FS_I(inode)->i_sem);
 	ret = F2FS_I(inode)->last_disk_size == i_size_read(inode);
 	up_read(&F2FS_I(inode)->i_sem);

fs/f2fs/inode.c

@@ -284,6 +284,10 @@ static int do_read_inode(struct inode *inode)
 		fi->i_crtime.tv_nsec = le32_to_cpu(ri->i_crtime_nsec);
 	}
 
+	F2FS_I(inode)->i_disk_time[0] = inode->i_atime;
+	F2FS_I(inode)->i_disk_time[1] = inode->i_ctime;
+	F2FS_I(inode)->i_disk_time[2] = inode->i_mtime;
+	F2FS_I(inode)->i_disk_time[3] = F2FS_I(inode)->i_crtime;
 	f2fs_put_page(node_page, 1);
 
 	stat_inc_inline_xattr(inode);
@@ -444,6 +448,10 @@ void update_inode(struct inode *inode, struct page *node_page)
 	if (inode->i_nlink == 0)
 		clear_inline_node(node_page);
 
+	F2FS_I(inode)->i_disk_time[0] = inode->i_atime;
+	F2FS_I(inode)->i_disk_time[1] = inode->i_ctime;
+	F2FS_I(inode)->i_disk_time[2] = inode->i_mtime;
+	F2FS_I(inode)->i_disk_time[3] = F2FS_I(inode)->i_crtime;
 }
 
 void update_inode_page(struct inode *inode)