Re: [GIT PULL] f2fs update for 6.8-rc1

[Jaegeuk Kim]

On 01/12, Al Viro wrote:
> On Thu, Jan 11, 2024 at 09:05:51PM -0800, Linus Torvalds wrote:
> > On Thu, 11 Jan 2024 at 10:28, Jaegeuk Kim <jaegeuk@xxxxxxxxxx> wrote:
> > >
> > >   git://git.kernel.org/pub/scm/linux/kernel/git/jaegeuk/f2fs.git tags/f2fs-for-6.8-rc1
> > 
> > Hmm. I got a somewhat confusing conflict in f2fs_rename().
> > 
> > And honestly, I really don't know what the right resolution is. What I
> > ended up with was this:
> > 
> >         if (old_is_dir) {
> >                 if (old_dir_entry)
> >                         f2fs_set_link(old_inode, old_dir_entry,
> >                                                 old_dir_page, new_dir);
> >                 else
> >                         f2fs_put_page(old_dir_page, 0);
> 
> Where would you end up with old_dir_page != NULL and old_dir_entry == NULL?
> old_dir_page is initialized to NULL and the only place where it's altered
> is
>                 old_dir_entry = f2fs_parent_dir(old_inode, &old_dir_page);
> Which is immediately followed by
>                 if (!old_dir_entry) {
>                         if (IS_ERR(old_dir_page))
>                                 err = PTR_ERR(old_dir_page);
>                         goto out_old;
>                 }
> so we are *not* going to end up at that if (old_is_dir) in that case.

It seems [1] changed the condition of getting old_dir_page reference as below,
which made f2fs_put_page(old_dir_page, 0) voided.

-       if (S_ISDIR(old_inode->i_mode)) {
+       if (old_is_dir && old_dir != new_dir) {
                old_dir_entry = f2fs_parent_dir(old_inode, &old_dir_page);
                if (!old_dir_entry) {
                        if (IS_ERR(old_dir_page))

[1] 7deee77b993a ("f2fs: Avoid reading renamed directory if parent does not change")

> 
> Original would have been more clear as
> 	if (old_is_dir) {
> 		if (old_dir != new_dir) {
> 			/* we have .. in old_dir_page/old_dir_entry */
> 			if (!whiteout)
> 	                        f2fs_set_link(old_inode, old_dir_entry,
>                                                 old_dir_page, new_dir);
> 			else
> 	                        f2fs_put_page(old_dir_page, 0);
> 		}
>                 f2fs_i_links_write(old_dir, false);
> 	}
> - it is equivalent to what that code used to do.  And "don't update ..
> if we are leaving a whiteout behind" was teh bug fixed by commit
> in f2fs tree...
> 
> The bottom line: your variant is not broken, but only because
> f2fs_put_page() starts with
> static inline void f2fs_put_page(struct page *page, int unlock)
> {
>         if (!page)
>                 return;
> 
> IOW, you are doing f2fs_put_page(NULL, 0), which is an explicit no-op.