linux-kernel - Re: [BUG] bug when enabling VM DEBUG

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Date:	Wed, 12 May 2010 12:10:39 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Robert Hancock <hancockrwd@...il.com>
Cc:	saeed bishara <saeed.bishara@...il.com>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	DE/ATA development list <linux-ide@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Jeff Garzik <jeff@...zik.org>,
	Sebastian Andrzej Siewior <sebastian@...akpoint.cc>
Subject: Re: [BUG] bug when enabling VM DEBUG

On Wed, 2010-05-12 at 03:41 +0100, Robert Hancock wrote:
> On 05/11/2010 09:27 AM, saeed bishara wrote:
> > Jeff,
> > seems that the libata do pio to buffer which was allocated with
> > kmalloc, and under arm arch, the flush_dcache_page() is needed to
> > prevent cache aliasing, the later function calls the page_mapping
> > which falls on PageSlab(page)
> >
> > as the flush_dcache_page() is needed to prevent aliasing, it can be
> > skipped if the page is Slab as such pages are used only by the kernel.
> > here a suggested patch:
> >
> > --- a/drivers/ata/libata-sff.c
> > +++ b/drivers/ata/libata-sff.c
> > @@ -894,7 +894,7 @@ static void ata_pio_sector(struct ata_queued_cmd *qc)
> >                                         do_write);
> >          }
> >
> > -       if (!do_write)
> > +       if (!do_write&&  !PageSlab(page))
> >                  flush_dcache_page(page);
> 
> I would think that check belongs inside flush_dcache_page itself, rather
> than forcing every driver to include it..

Sebastian (cc'ed) reported this as well for MIPS.

I think it makes sense for this check to be done in the
flush_dcache_page() function.

-- 
Catalin

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