Messages in this thread | | | Date | Wed, 12 Oct 2011 11:56:46 -0400 | From | Johannes Weiner <> | Subject | Re: [PATCH] mm/huge_memory: Clean up typo when copying user highpage |
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On Wed, Oct 12, 2011 at 10:39:36PM +0800, Hillf Danton wrote: > Hi Andrea > > When copying user highpage, the PAGE_SHIFT in the third parameter is a typo, > I think, and is replaced with PAGE_SIZE.
This is a pretty nasty data corruption bug, so 'clean up' might be a bit of an understatement ;-)
Nice catch.
Would you mind extending the changelog to include a problem description? Feel free to steal from this:
The THP copy-on-write handler falls back to regular-sized pages for a huge page replacement upon allocation failure or if THP has been individually disabled in the target VMA. The loop responsible for copying page-sized chunks accidentally uses multiples of PAGE_SHIFT instead of PAGE_SIZE as the byte offset into the original huge page, though, and the COW-breaking task ends up with a corrupt copy of the data.
> Signed-off-by: Hillf Danton <dhillf@gmail.com>
Acked-by: Johannes Weiner <jweiner@redhat.com>
> --- a/mm/huge_memory.c Sat Aug 13 11:45:14 2011 > +++ b/mm/huge_memory.c Wed Oct 12 22:26:15 2011 > @@ -829,7 +829,7 @@ static int do_huge_pmd_wp_page_fallback( > > for (i = 0; i < HPAGE_PMD_NR; i++) { > copy_user_highpage(pages[i], page + i, > - haddr + PAGE_SHIFT*i, vma); > + haddr + PAGE_SIZE * i, vma); > __SetPageUptodate(pages[i]); > cond_resched(); > }
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