linux-kernel - Re: [PATCH 1/2] fs: optimize mpage

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Message-ID: <20100604101848.GA6367@a1.tnic>
Date:	Fri, 4 Jun 2010 12:18:48 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Changli Gao <xiaosuo@...il.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] fs: optimize mpage_readpage()

From: Al Viro <viro@...IV.linux.org.uk>
Date: Fri, Jun 04, 2010 at 09:30:31AM +0100

> On Fri, Jun 04, 2010 at 10:13:22AM +0200, Borislav Petkov wrote:
> > > > > -	bio = do_mpage_readpage(bio, page, 1, &last_block_in_bio,
> > > > > +	bio = do_mpage_readpage(NULL, page, 1, &last_block_in_bio,
> 
> > Right, the uninitialized warning above happens when you remove the NULL
> > assignment, i.e.
> > 
> > struct bio *bio;
> > 
> > ...
> > 
> > bio = do_mpage_readpage(bio, ...)
> 
> WTF?  His patch does *NOT* leave you with bio = do_mpage_readpage(bio, ...),
> it replaces that with bio = do_mpage_readpage(NULL, ...).
> 
> Which variant has produced a warning?
> 
> > But(!), in the mpage_readpage(), bio _absolutely_ has to be NULL because
> > it is checked if being so later in do_mpage_readpage(), so this one is a
> > complete different story.
> > 
> > To cut a long story short, you're correct, gcc is b0rked when warning
> > about passing addresses of variables to functions which only write to
> > them.
> 
> To make it even shorter, you've misapplied the patch.  Correct?

Yes.

-- 
Regards/Gruss,
Boris.
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