On Mon, Apr 22, 2013 at 3:44 AM, Mike Qiu <qiudayu@xxxxxxxxxxxxxxxxxx> wrote: > 于 2013/4/22 16:04, Benjamin Herrenschmidt 写道: > >> On Mon, 2013-04-22 at 15:41 +0800, Mike Qiu wrote: >>> >>> Anyway, I think it's better to remove the check code as it is useless, >>> as it >>> will shows that this "NULL" pci_controller pointer may happen... >> >> Ok. It *might* still be worth adding a BUG_ON then in pci_bus_to_host() >> itself ... no big deal either way. > > OK, you mean the code will remain the same and my patch is worthless? > > Anyway, it will be OK for me. But I hope it can be accept for more stable > reason. This is powerpc code, so I'm kibitzing here, but it was cc'd to linux-pci :) There should be no way to get a struct pci_bus * where bus->sysdata (== "hose") is NULL. The sysdata pointer is always supplied to pci_create_root_bus() (or a similar interface that calls pci_create_root_bus()), so every root bus has a valid sysdata pointer. And every child bus inherits the sysdata pointer of its parent (in pci_alloc_child_bus()). Therefore, every pci_bus should have a valid sysdata pointer. So I think you should just remove even the existing "if (hose == NULL)" check. That way, if bus->sysdata actually *does* turn out to be NULL, we'll oops on the null pointer dereference, get a nice backtrace, and have a chance to fix the problem. Testing and returning an error means whatever bug or memory corruption caused the null pointer will most likely be ignored. Bjorn -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
