Re: [patch 1/3] mm: fix PageUptodate memorder

[Nick Piggin]

Andrew Morton wrote:
> On Tue,  6 Feb 2007 09:02:11 +0100 (CET) Nick Piggin <npiggin@xxxxxxx> wrote:
>
>
> > +static inline void __SetPageUptodate(struct page *page)
> > +{
> > +#ifdef CONFIG_S390
> > 	if (!test_and_set_bit(PG_uptodate, &page->flags))
> > 		page_test_and_clear_dirty(page);
> > -}
> > #else
> > -#define SetPageUptodate(page)	set_bit(PG_uptodate, &(page)->flags)
> > +	/*
> > +	 * Memory barrier must be issued before setting the PG_uptodate bit,
> > +	 * so all previous writes that served to bring the page uptodate are
> > +	 * visible before PageUptodate becomes true.
> > +	 *
> > +	 * S390 is guaranteed to have a barrier in the test_and_set operation
> > +	 * (see Documentation/atomic_ops.txt).
> > +	 *
> > +	 * XXX: does this memory barrier need to be anything special to
> > +	 * handle things like DMA writes into the page?
> > +	 */
> > +	smp_wmb();
> > +	set_bit(PG_uptodate, &(page)->flags);
> > #endif
> > +}
> > +
> > +static inline void SetPageUptodate(struct page *page)
> > +{
> > +	WARN_ON(!PageLocked(page));
> > +	__SetPageUptodate(page);
> > +}
> > +
> > +static inline void SetNewPageUptodate(struct page *page)
> > +{
> > +	__SetPageUptodate(page);
> > +}
>
>
> I was panicing for a minute when I saw that __SetPageUptodate() in there.
>
> Conventionally the __SetPageFoo namespace is for nonatomic updates to
> page->flags.  Can we call this something different?

Duh, of course, sorry.

> What a fugly patchset :(

Fugly problem. One could fix it by always locking the page, but I was
worried about Hugh flaming me if I tried that ;)

--
SUSE Labs, Novell Inc.
Send instant messages to your online friends http://au.messenger.yahoo.com 
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/