On Mon, Apr 11, 2011 at 11:49:30AM -0400, Alan Stern wrote:
> On Mon, 11 Apr 2011, Roedel, Joerg wrote:
>
> > On Mon, Apr 11, 2011 at 02:26:00AM -0400, Borislav Petkov wrote:
> > > You mean 2.6.39-rc2 right? I'm asking because I hit the same warning
> > > with 39-rc2 now too but it didn't appear with .38 - so it has to have
> > > snuck in after the merge window. If so, you don't need the stable tag.
> >
> > You were right, just tested plain 2.6.38 and it doesn't happen. So I
> > removed the stable tag. Here is the updated patch.
>
> ...
>
> > --- a/drivers/usb/host/pci-quirks.c
> > +++ b/drivers/usb/host/pci-quirks.c
> > @@ -84,65 +84,92 @@ int usb_amd_find_chipset_info(void)
> > {
>
> ...
>
> > +commit:
> > +
> > + spin_lock_irqsave(&amd_lock, flags);
> > + if (amd_chipset.probe_count > 0) {
> > + /* race - someone else was faster - drop devices */
> > +
> > + /* Mark that we where here */
> > + amd_chipset.probe_count++;
>
> This line should be moved above the "if" statement, since you always
> want to increment the count.
No, probe_count can't be incremented here because the probe is not
finished yet. If another thread jumps in after the lock is released and
detects probe_count > 0 while the probe hasn't happened the quirk will
fail. So we need to make sure that amd_chipset.probe_count does not
become > 0 before the probe is finished.
>
> > + ret = amd_chipset.probe_result;
> > +
> > + spin_unlock_irqrestore(&amd_lock, flags);
> > +
> > + if (info.nb_dev)
> > + pci_dev_put(info.nb_dev);
> > + if (info.smbus_dev)
> > + pci_dev_put(info.smbus_dev);
> > +
> > + } else {
> > + /* no race - commit the result */
> > + info.probe_count++;
>
> This isn't right, because info.probe_count was initialized to 0. Maybe
> amd_chipset.probe_count should be made into a separate variable, not a
> part of the structure, like amd_lock.
The purpose of the struct is structuring of data. In theory all of its
members could be turned into global variables. The amd_lock is different
because it does not only protect the struct but also access to the
hardware while the quirk is applied/unapplied.
Joerg
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