Catalin Marinas wrote:
> On Wed, 2010-05-12 at 12:53 +0100, Sebastian Andrzej Siewior wrote:
> > * Catalin Marinas | 2010-05-12 12:10:39 [+0100]:
> >
> > >> > --- 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.
> > Thx. The patch above looks what I've sent a while ago. Jeff was going to
> > merge it afaik.
> >
> > >I think it makes sense for this check to be done in the
> > >flush_dcache_page() function.
> >
> > Why should flush_dcache_page() not flush pages you tell it?
> > From Documentation/cachetlb.txt:
> > | NOTE: This routine need only be called for page cache pages
> > | which can potentially ever be mapped into the address
> > | space of a user process. So for example, VFS layer code
> > | handling vfs symlinks in the page cache need not call
> > | this interface at all.
> >
> > A page from slab or stack is not going to see the sky of user land and
> > therefore it should not be fed into flush_dcache_page().
>
> You are right :), so fixing the driver is the best approach.
It worries me that a driver has any knowledge of the PageSlab() flag,
though. Especially uncommented knowledge. That flag seems VM
internal, and it's conceptually iffy: Kernel code using
get_free_pages() and using that for I/O also does not see the sky of
user land.
If all the PIO drivers have to be changed, I'd be happier with:
flush_dcache_page_for_pio()
which wraps the check, explains it, and provides a single place to
change if needed.
-- Jamie
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