Messages in this thread | | | Date | Tue, 7 Apr 2009 22:17:08 +0200 | From | Johannes Weiner <> | Subject | Re: [PATCH] [8/16] POISON: Add various poison checks in mm/memory.c |
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On Tue, Apr 07, 2009 at 09:31:45PM +0200, Andi Kleen wrote: > On Tue, Apr 07, 2009 at 09:03:30PM +0200, Johannes Weiner wrote: > > On Tue, Apr 07, 2009 at 05:10:05PM +0200, Andi Kleen wrote: > > > > > > Bail out early when poisoned pages are found in page fault handling. > > > Since they are poisoned they should not be mapped freshly > > > into processes. > > > > > > This is generally handled in the same way as OOM, just a different > > > error code is returned to the architecture code. > > > > > > Signed-off-by: Andi Kleen <ak@linux.intel.com> > > > > > > --- > > > mm/memory.c | 7 +++++++ > > > 1 file changed, 7 insertions(+) > > > > > > Index: linux/mm/memory.c > > > =================================================================== > > > --- linux.orig/mm/memory.c 2009-04-07 16:39:39.000000000 +0200 > > > +++ linux/mm/memory.c 2009-04-07 16:39:39.000000000 +0200 > > > @@ -2560,6 +2560,10 @@ > > > goto oom; > > > __SetPageUptodate(page); > > > > > > + /* Kludge for now until we take poisoned pages out of the free lists */ > > > + if (unlikely(PagePoison(page))) > > > + return VM_FAULT_POISON; > > > + > > > > When memory_failure() hits a page still on the free list > > It won't free it then. Later on it will take it out of the free lists, > but that code is not written yet. > > > (!page_count()) then the get_page() in memory_failure() will trigger a > > VM_BUG. So either this check is unneeded or it should be > > So no bug > > get_page_unless_zero() in memory_failure()? > > That's not what this is handling. The issue is that sometimes > the process can still freeing it and we need to make sure it > never hits the free lists.
I think we missed each other here. I wasn't talking about _why_ you take that reference -- that is clear. But I see these two possibilities:
a) memory_failure() is called on a page on the free list, the get_page() will trigger a bug because the refcount is 0
b) if that is not possible, the above check is not needed
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