On Thu, Oct 24, 2013 at 11:13 PM, Yinghai Lu <yinghai@xxxxxxxxxx> wrote: > On Thu, Oct 24, 2013 at 8:33 PM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote: >> >>>>> Bisection points to 928bea964827d7824b548c1f8e06eccbbc4d0d7d . >>>> >>>> This is "PCI: Delay enabling bridges until they're needed" by Yinghai. >>> >>> that double disabling should be addressed by: >>> >>> https://lkml.org/lkml/2013/4/25/608 >>> >>> [PATCH] PCI: Remove duplicate pci_disable_device for pcie port >> >> I'll look at that patch again. I had some questions about it the >> first time, but perhaps it makes more sense after 928bea9648 has been >> applied. >> >> Andreas originally reported a GPF oops in pci_pme_list_scan(). I >> posted a refcounting patch, which made the problem go away, but I >> can't explain why, and I don't want to apply it without understanding >> that. Decoding his oops shows this: >> >> 24: 0f 1f 00 nopl (%rax) >> 27: 48 8b 50 10 mov 0x10(%rax),%rdx >> 2b:* 48 8b 52 38 mov 0x38(%rdx),%rdx <-- trapping instruction >> 2f: 48 85 d2 test %rdx,%rdx >> >> %rax is the pci_dev pointer, so 0x10(%rax) is the dev->bus pointer, >> which we put in %rdx. The oops says %rdx = 6b6b6b6b6b6b6b6b, which is >> POISON_FREE, so I think we loaded dev->bus out of a struct pci_dev >> that has already been freed. >> >> pci_pme_list_scan() holds pci_pme_list_mutex while it traverses >> pci_pme_list, and the pci_stop_and_remove_bus_device() path removes >> the pci_dev by calling pci_pme_active(), which also holds >> pci_pme_list_mutex, so I don't understand how pci_pme_list_scan() can >> see a pci_dev that has already been freed. >> >> If I understand Andreas correctly, 928bea9648 also fixes the crash, >> even without my refcounting change. Can you explain why? > > 928bea will make the dev->enable_cnt increase wrongly, as we have > pci_enable_device for child > pci_enable_bridge for parent > pci_enable_bridge for grandparent > pci_enable_device for grandparent > pci_enable_device for parent > pci_enable_brdige for grandparent > pci_enable_device for grandparent. > ... > > in that case grandprent will be enabled two times, and will enable_cnt will have > extra increase. > > so later pci_disable_device will not really call do_pci_disable_device > do the really work, as enable_cnt still big. > > solution could be: > let pci_enable_bridge call __pci_enable_device. > and __pci_enable_device will not call pci_enable_bridge. Sorry, I didn't understand this. Is this supposed to be an explanation of how 928bea fixes the oops that Andreas saw? If so, can you be a little more explicit about when the pci_dev got freed and when pci_pme_list_scan() walked the list and accessed the freed area? 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
