linux-ext4 - Re: dead/wrong code in ext3/4

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Message-ID: <20120702170959.GJ6679@quack.suse.cz>
Date:	Mon, 2 Jul 2012 19:09:59 +0200
From:	Jan Kara <jack@...e.cz>
To:	Andrew Perepechko <anserper@...ru>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: dead/wrong code in ext3/4_releasepage()

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@...e.cz>
SUSE Labs, CR
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