Re: acpi_cpu_freq_init warning...

Greg KH
2008-05-06T20:21:25Z

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.

> Whoops, sorry. You are right.
>
> diff -puN drivers/base/sys.c~fix-sys-bogus-warning drivers/base/sys.c
> --- linux-2.6/drivers/base/sys.c~fix-sys-bogus-warning 2008-05-07 03:51:00.000000000 +0900
> +++ linux-2.6-hirofumi/drivers/base/sys.c 2008-05-07 04:01:14.000000000 +0900
> @@ -175,8 +175,7 @@ int sysdev_driver_register(struct sysdev
> }
>
> /* Check whether this driver has already been added to a class. */
> - if ((drv->entry.next != drv->entry.prev) ||
> - (drv->entry.next != NULL)) {
> + if (drv->entry.next && !list_empty(&drv->entry)) {

Did you try this patch out?

I say rip the whole thing out, it was added to try to make some bugs in
upper layers more obvious, but if it can't be correct, I have no
objection to removing the thing. Other bad things happen later on if
the developer messes this one up, this is not a 'user can cause this'
type of error at all.

thanks,

greg k-h