On Tue, Aug 23, 2016 at 10:22:59AM +0800, wangyijing wrote: > 在 2016/8/23 1:28, Bjorn Helgaas 写道: > > On Thu, Jun 23, 2016 at 07:42:18PM +0800, Yijing Wang wrote: > >> pci_host_bridge holds the top resources(IO port/Mem/bus), > >> now we release pci_host_bridge resources in > >> acpi_pci_root_release_info() which would be called when > >> pci_host_bridge device refcount reach 0. In some cases, > >> pci_host_bridge refcount cannot reach 0 after we remove > >> pci root bus in pci_remove_root_bus(). > > > > Did you figure out *why* the host bridge refcount is non-zero? > > That seems like it could be part of the problem. > > 1. pci_create_root_bus() //root bus get a refcount of hostbridge， put the > refcount when root bus release(bus dev refcount == 0); > 2. pci_alloc_dev() //pci dev get a refcount of pci_bus, put the refcount > when pci_dev release(pci_dev refcount == 0) > 3. some upper driver could get the pci dev refcount(e.g. we found if we mount a fs in mptsas disk, the mptsas pci dev refcount would be added) > > 4. if we start remove the root bus before umount, in this case, the mptsas pci dev refcount won't reach 0, so as the step 1 and 2 show, > the root bus and host bridge refcount won't reach 0 too. > > > > > > You're moving some release_resource() calls from pci_root.c to > > host-bridge.c. Where are the corresponding insert or request resource > > calls? It's more maintainable if we keep the insert and remove paths > > close in the code. > > > >> Then if we want to > >> hot add pci root bus, we cannot use pci_host_bridge > >> resources because of conflicts with old resources which are > >> still in system. I think this is not reasonable. > >> > >> 1. For pci devices, we would release their resources in > >> pci_destroy_dev() regardless of pci device refcount. > >> 2. When we try to remove pci root bus, there is no devices > >> need to use the pci_host_bridge resources again, release > >> pci_host_bridge resources is safe. > >> 3. In some cases, users woule make mistake, for example, > >> user get a pci device(increase refcount), but forget to > >> put this device, then if we do hotplug pci root bus, > >> it would make all pci devices cannot work after hot add. > > > > Can you explain this a little more? Are you talking about a *driver* > > that forgets to put the device? > > Yes, may some pci drivers make a mistake, the refcount control the device object > release is fine, but I think move the mem resource release out is better. If this is caused by driver bugs, I think we need to fix the driver bugs. So far all I see here is "it works when I do this." What we need is an argument for "it's correct to do this." It's certainly possible that you're already making that argument and I'm just not understanding it. > >> I found this issue in the following case: > >> 1. I have a raid pci device in my system; > >> 2. I mount a disk which connect to this raid. > >> 3. hot remove the pci root bus. > >> 4. hot add the pci root bus. > >> 5. found the resource conflicts for the children pci devices under this root bus. > >> > >> pci_root_bus increase a refcount at pci_host_bridge. > >> pci_root_bus decrease a refcount at pci_host_bridge in > >> release_pcibus_dev() when pci_root_bus device refcount reach 0. > >> > >> pci_dev increase a refcount at pci_bus in pci_alloc_dev(). > >> pci_dev decrease a refcount at pci_bus in pci_release_dev() > >> when pci_dev refcount reach 0. > >> > >> If any pci device refcount cannot reach 0, then its pci_bus > >> refcount cannot reach 0 too, the result is pci_host_bridge > >> refcount cannot reach 0. > > > > . > > > -- 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
