Re: [patch] mm, page_alloc: make first_page visible beforePageTail

[David Rientjes]

On Tue, 4 Feb 2014, Andrew Morton wrote:

> > Commit bf6bddf1924e ("mm: introduce compaction and migration for ballooned 
> > pages") introduces page_count(page) into memory compaction which 
> > dereferences page->first_page if PageTail(page).
> > 
> > Introduce a store memory barrier to ensure page->first_page is properly 
> > initialized so that code that does page_count(page) on pages off the lru 
> > always have a valid p->first_page.
> 
> Could we have a code comment please?  Even checkpatch knows this rule!
> 

Ok.

> > Reported-by: Holger Kiehl <Holger.Kiehl@xxxxxx>
> 
> What did Holger report?
> 

A once-in-five-years NULL pointer dereference on the aforementioned 
page_count(page).
--
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/