linux-kernel - Re: [ 04/21] target/pscsi: Fix page increment

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Message-ID: <20130318053519.GE6232@hj.localdomain>
Date:	Mon, 18 Mar 2013 13:35:19 +0800
From:	Asias He <asias@...hat.com>
To:	Ben Hutchings <ben@...adent.org.uk>
Cc:	Nicholas Bellinger <nab@...ux-iscsi.org>,
	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [ 04/21] target/pscsi: Fix page increment

On Sat, Mar 16, 2013 at 02:10:22AM +0000, Ben Hutchings wrote:
> On Tue, 2013-03-12 at 15:44 -0700, Greg Kroah-Hartman wrote:
> > 3.0-stable review patch.  If anyone has any objections, please let me know.
> > 
> > ------------------
> > 
> > From: Asias He <asias@...hat.com>
> > 
> > commit 472b72f2db7831d7dbe22ffdff4adee3bd49b05d upstream.
> > 
> > The page++ is wrong. It makes bio_add_pc_page() pointing to a wrong page
> > address if the 'while (len > 0 && data_len > 0) { ... }' loop is
> > executed more than one once.
> > 
> > Signed-off-by: Asias He <asias@...hat.com>
> > Signed-off-by: Nicholas Bellinger <nab@...ux-iscsi.org>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > 
> > ---
> >  drivers/target/target_core_pscsi.c |    1 -
> >  1 file changed, 1 deletion(-)
> > 
> > --- a/drivers/target/target_core_pscsi.c
> > +++ b/drivers/target/target_core_pscsi.c
> > @@ -1210,7 +1210,6 @@ static int __pscsi_map_task_SG(
> >  				bio = NULL;
> >  			}
> >  
> > -			page++;
> >  			len -= bytes;
> >  			data_len -= bytes;
> >  			off = 0;
> 
> So in case a fragment crosses a page boundary, we wrap around to the
> beginning of the same page?  That doesn't look right.

If the fragment crosses a page boundary, what is the correct page
for it?

Nicholas, can we assume sg->length + sg->offset should be less than PAGE_SIZE here?

> Ben.
> 
> -- 
> Ben Hutchings
> It is easier to change the specification to fit the program than vice versa.

-- 
Asias
--
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