Re: [Xen-devel] Re: Balloon driver crash

[M A Young <m.a.young@xxxxxxxxxxxx>]

On Tue, 8 Jun 2010, Ian Campbell wrote:

> On Mon, 2010-06-07 at 20:29 +0100, M A Young wrote:
> > On Thu, 3 Jun 2010, Dave McCracken wrote:
> >
> > > On Thursday, June 03, 2010, Ian Campbell wrote:
> > > > > This seems to be about line 343 of drivers/xen/balloon.c in the
> > > > > subroutine  decrease_reservation which is
> > > > >
> > > > >                  for (j = 0; j < balloon_npages; j++, lpfn++, mfn++) {
> > > > >                          if ((discontig_frame_list[j] =
> > > > > pfn_to_mfn(lpfn))
> > > > >
> > > > > != mfn)
> > > > >
> > > > >                                  discontig_free = 1;
> > > > >
> > > > >                          set_phys_to_machine(lpfn, INVALID_P2M_ENTRY);
> > > > >
> > > > > /* here */                  if (!PageHighMem(page)) {
> > > > >
> > > > >                                  ret = HYPERVISOR_update_va_mapping(
> > > > >                                          (unsigned long)__va(lpfn <<
> > > > >
> > > > > PAGE_SHIFT),
> > > > >
> > > > >                                          __pte_ma(0), 0);
> > > > >                                  BUG_ON(ret);
> > > > >                          }
> > > > >                  }
> > > > >
> > > > >
> > > > > > From what I can tell page is meaningless in this context as it is just
> > > > > a temporary variable used in the previous loop, so I would
> > > > > guess that PageHighMem should be checking something else, or page should
> > > > > be set somewhere eg. at a guess page=pfn_to_page(lpfn);
> > > > That would be my guess also. CCing Dave McCracken who looks to have
> > > > introduced this code in 0e898d5e "Add hugepage support to balloon
> > > > driver"
> > > Yes, that is definitely an error.  The offending line should be
> > >
> > >         if (!PageHighMem(pfn_to_page(lpfn))) {
> > >
> > > Dave McCracken
> > > Oracle Corp.
> > I have tested the corrected line and it does fix the crash I was seeing.
> Please can one of you generate a patch and send it to the list.
Attached.

        Michael Young

Attachment: balloon.fix.patch
Description: Text document

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