linux-kernel - Re: [patch 68/85] fs: symlink write

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Message-ID: <20090116025310.GH17810@wotan.suse.de>
Date:	Fri, 16 Jan 2009 03:53:10 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Greg KH <greg@...ah.com>
Cc:	linux-kernel@...r.kernel.org, stable@...nel.org,
	Justin Forbes <jmforbes@...uxtx.org>,
	Zwane Mwaikambo <zwane@....linux.org.uk>,
	Theodore Ts'o <tytso@....edu>,
	Randy Dunlap <rdunlap@...otime.net>,
	Dave Jones <davej@...hat.com>,
	Chuck Wolber <chuckw@...ntumlinux.com>,
	Chris Wedgwood <reviews@...cw.f00f.org>,
	Michael Krufky <mkrufky@...uxtv.org>,
	Chuck Ebbert <cebbert@...hat.com>,
	Domenico Andreoli <cavokz@...il.com>, Willy Tarreau <w@....eu>,
	Rodrigo Rubira Branco <rbranco@...checkpoint.com>,
	Jake Edge <jake@....net>, Eugene Teo <eteo@...hat.com>,
	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Subject: Re: [patch 68/85] fs: symlink write_begin allocation context fix

On Thu, Jan 15, 2009 at 02:31:17PM -0800, Greg KH wrote:
> On Thu, Jan 15, 2009 at 02:01:36PM -0800, Greg KH wrote:
> > 2.6.27-stable review patch.  If anyone has any objections, please let us know.
> 
> Hm, I think I got the backport of this patch wrong in two place:
> 
> > --- a/mm/filemap.c
> > +++ b/mm/filemap.c
> > @@ -2033,7 +2033,7 @@ int pagecache_write_begin(struct file *f
> >  		struct inode *inode = mapping->host;
> >  		struct page *page;
> >  again:
> > -		page = __grab_cache_page(mapping, index);
> > +		page = grab_cache_page_write_begin(mapping, index, flags);
> 
> I think this shouldn't be "flags", but 0, right?

I think flags is right. That way, a caller of pagecache_write_begin (eg. page_symlink)
can instruct it with AOP_FLAG_NOFS to prevent grab_cache_page from doing a GFP_KERNEL
allocation.

> > @@ -2263,7 +2268,7 @@ static ssize_t generic_perform_write_2co
> >  			break;
> >  		}
> >  
> > -		page = __grab_cache_page(mapping, index);
> > +		page = grab_cache_page_write_begin(mapping, index, GFP_KERNEL);
> 
> And this one?  Is GFP_KERNEL ok, or 0?
> 
> Nick, your thoughts?

This should be 0. grab_cache_page_write_begin takes write_begin aop flags rather
than regular gfp flags (it's a bit confusing, sorry :P). 0 ~= GFP_KERNEL (wheras
AOP_FLAG_NOFS ~= GFP_NOFS). So you have the right idea ;)

Thanks,
Nick
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