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Date: Fri, 12 Jan 2024 07:12:42 +0000
From: Al Viro <viro@zeniv.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Linux F2FS Dev Mailing List <linux-f2fs-devel@lists.sourceforge.net>
Subject: Re: [GIT PULL] f2fs update for 6.8-rc1
Message-ID: <20240112071242.GA1674809@ZenIV>
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On Thu, Jan 11, 2024 at 09:05:51PM -0800, Linus Torvalds wrote:
> On Thu, 11 Jan 2024 at 10:28, Jaegeuk Kim <jaegeuk@kernel.org> 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.

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.