Re: acpi_cpu_freq_init warning...

Linus Torvalds
2008-05-06T20:28:51Z

On Tue, 6 May 2008, Greg KH wrote:

> On Wed, May 07, 2008 at 04:02:53AM +0900, OGAWA Hirofumi wrote:
> > Linus Torvalds <torvalds@linux-foundation.org> writes:
> >
> > > On Tue, 6 May 2008, OGAWA Hirofumi wrote:
> > >> - if ((drv->entry.next != drv->entry.prev) ||
> > >> + if ((drv->entry.next != drv->entry.prev) &&
> > >> (drv->entry.next != NULL)) {
> > >
> > > Umm. That code still makes no sense.
> > >
> > > The "drv->entry.next == drv->entry.prev" condition will trigger under
> > > *three* different circumstances:
> > >
> > > - next/prev == NULL (uninitialized). Checked for by the explicit check
> > > against NULL.
> > >
> > > - list empty (both next/prev point back to itself), which I assume the
> > > check was *meant* for.
> > >
> > > - list has only *one* entry, when next/prev both point to the list head.
> > >
> > > and I'm pretty damn sure that whoever wrote that code didn't mean that
> > > last one, but who knows..
> > >
> > > The fact is, looking at next/prev this way is a sure way to have bugs.
> > >
> > > What is that PoS *trying* to test for? I assume it is meant to test for
> > >
> > > /* Is the list initialized and non-empty? */
> > > if (drv->entry.next && !list_empty(&drv->entry)) {
> > > ...
> > >
> > > and dammit, just doing it that way is shorter and simpler.
>
> But I don't think that will work as others have pointed out, this
> structure's list field isn't initialized yet.

Umm. And what do you think the test for drv->entry.next is there for?

Ie the assumption is that it's at least zeroed out, if it's not
initialized.

Now, admittedly it could be *total* crud, but if so, I'd seriously suggest
just fixing the callers, rather than passing totally uninitialized
structures with random crap in it around.

Linus