Messages in this thread | | | Date | Wed, 5 Feb 2014 09:42:35 +0100 | From | Michal Hocko <> | Subject | Re: [patch v2] mm, page_alloc: make first_page visible before PageTail |
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On Tue 04-02-14 16:22:53, David Rientjes 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. > > Reported-by: Holger Kiehl <Holger.Kiehl@dwd.de> > Signed-off-by: David Rientjes <rientjes@google.com> > --- > v2: with commentary, per checkpatch > > mm/page_alloc.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -369,9 +369,11 @@ void prep_compound_page(struct page *page, unsigned long order) > __SetPageHead(page); > for (i = 1; i < nr_pages; i++) { > struct page *p = page + i; > - __SetPageTail(p); > set_page_count(p, 0); > p->first_page = page; > + /* Make sure p->first_page is always valid for PageTail() */ > + smp_wmb(); > + __SetPageTail(p);
Where is the pairing smp_rmb? I would expect it in comound_head.
> } > } >
-- Michal Hocko SUSE Labs
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