Re: dead/wrong code in ext3/4_releasepage()

Jan Kara
2012-07-02T17:10:01Z

On Fri 29-06-12 20:52:51, Andrew Perepechko wrote:
> Hello!
>
> The implementation of ext4_releasepage() for many kernel versions
> (as well as current git) is the following:
>
> static int ext4_releasepage(struct page *page, gfp_t wait)
> {
> journal_t *journal = EXT4_JOURNAL(page->mapping->host);
>
> trace_ext4_releasepage(page);
>
> WARN_ON(PageChecked(page));
> if (!page_has_buffers(page))
> return 0;
> if (journal)
> return jbd2_journal_try_to_free_buffers(journal,
> page, wait);
> else
> return try_to_free_buffers(page);
> }
>
> The "if (!page_has_buffers(page))" check seems to be attempting to
> handle the "nobh" case. However, the correct return value for this case
> seems to be 1 (success), not 0 (failure).
>
> This does not lead to oom or any similar issue since calls to
> try_to_release_page()
> are accompanied by page_has_private() checks.
>
> If ->release_page() can be called without a prior check, then
> the return code is wrong. Otherwise, the check is dead code.
>
> What do you think?
The check is a dead code because ->release_page() is called only if
PagePrivate bit is set.

Honza
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR