Re: acpi_cpu_freq_init warning...

OGAWA Hirofumi
2008-05-06T19:03:19Z

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.

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)) {
printk(KERN_WARNING "sysdev: class %s: driver (%p) has already"
" been registered to a class, something is wrong, but "
"will forge on!\n", cls->name, drv);
_
--
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>