On Friday 27 July 2007 21:38:53 Andrew Morton wrote:
> > > > +static ssize_t ssb_pci_attr_sprom_show(struct device *pcidev,
> > > > + struct device_attribute *attr,
> > > > + char *buf)
> > > > +{
> > > > + struct pci_dev *pdev = container_of(pcidev, struct pci_dev,
> > > > dev);
> > > > + struct ssb_bus *bus;
> > > > + u16 *sprom;
> > > > + int err = -ENODEV;
> > > > + ssize_t count = 0;
> > > > +
> > > > + bus = ssb_pci_dev_to_bus(pdev);
> > > > + if (!bus)
> > > > + goto out;
> > > > + err = -ENOMEM;
> > > > + sprom = kcalloc(SSB_SPROMSIZE_WORDS, sizeof(u16), GFP_KERNEL);
> > > > + if (!sprom)
> > > > + goto out;
> > > > +
> > > > + err = -ERESTARTSYS;
> > > > + if (mutex_lock_interruptible(&bus->pci_sprom_mutex))
> > > > + goto out_kfree;
> > > > + sprom_do_read(bus, sprom);
> > > > + mutex_unlock(&bus->pci_sprom_mutex);
> > > > +
> > > > + count = sprom2hex(sprom, buf, PAGE_SIZE);
> > > > + err = 0;
> > > > +
> > > > +out_kfree:
> > > > + kfree(sprom);
> > > > +out:
> > > > + return err ? err : count;
> > > > +}
> > >
> > > The mutex_lock_interruptible() looks fishy. Some commented explanation of
> > > what it's doing would be good here. It's quite unobvious to this reader.
> > > Cheesy deadlock avoidance? Hope not.
> >
> > No, it's simply to avoid writing the SPROM concurrently.
> > SPROM writing is hairy and we must make sure here that
> > we are the only one accessing the whole bus. We do that
> > by suspending all devices and taking a lock to protect
> > the SPROM from write concurrency.
>
> Sure, but why is the locking interruptible rather than plain old
> mutex_lock()?
Hm, well. We hold this mutex for several seconds, as writing takes
this long. So I simply thought it was worth allowing the waiter
to interrupt here. If you say that's not an issue, I'll be happy
to use mutex_lock() and reduce code complexity in this area.
--
Greetings Michael.
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