Re: [Xen-devel] [PATCH] libxl: do not try to detach pci device when none attached

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Fri, 10 Jun 2011, Marek Marczykowski wrote:
> On 10.06.2011 12:44, Stefano Stabellini wrote:
> > On Fri, 10 Jun 2011, Marek Marczykowski wrote:
> >> # HG changeset patch
> >> # User Marek Marczykowski <marmarek@xxxxxxxxxxxx>
> >> # Date 1307662302 -7200
> >> # Node ID 88f67b423c89f4bd604837b9eae2483dad5ebb0d
> >> # Parent  4b392511ae0840fba66c40aa2788dc1ff402b6e8
> >> libxl: do not try to detach pci device when none attached
> >>
> >> Fixes SEGV on domain destroy
> >>
> >> Signed-off-by: Marek Marczykowski <marmarek@xxxxxxxxxxxx>
> >>
> >> diff --git a/tools/libxl/libxl_pci.c b/tools/libxl/libxl_pci.c
> >> --- a/tools/libxl/libxl_pci.c
> >> +++ b/tools/libxl/libxl_pci.c
> >> @@ -1039,6 +1039,8 @@ int libxl_device_pci_shutdown(libxl_ctx 
> >>      rc = libxl_device_pci_list_assigned(ctx, &pcidevs, domid, &num);
> >>      if ( rc )
> >>          return rc;
> >> +    if ( num == 0 )
> >> +        return 0;
> >>      for (i = 0; i < num; i++) {
> >>          /* Force remove on shutdown since, on HVM, qemu will not always
> >>           * respond to SCI interrupt because the guest kernel has shut 
> >> down the
> > 
> > Is the problem here that num is 0 and pcidevs is uninitialized?
> > If so, would this patch solve the problem you are seeing?
> 
> No, when there is no PCI devs, libxl_device_pci_list_assigned exists
> earlier - before allocating memory for pcidevs.

Sorry, but I still don't understand.

If num is 0, it won't enter the following loop anyway, the only
other operation in libxl_device_pci_shutdown is free(pcidevs) and
pcidevs should be NULL so nothing bad should happen.

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