On Wed, Jul 04, 2018 at 11:34:55AM +0200, Paolo Bonzini wrote: > On 04/07/2018 08:42, Cédric Le Goater wrote: > > On 07/04/2018 04:26 AM, Peter Xu wrote: > >> On Tue, Jul 03, 2018 at 02:45:24PM +0200, Cédric Le Goater wrote: > >>> On 07/02/2018 05:57 AM, Peter Xu wrote: > >>>> On Sun, Jul 01, 2018 at 07:19:53PM +0200, Cédric Le Goater wrote: > >>>>> When a PCI device is unplugged, the PCI memory regions are deleted > >>>>> before the optional ROM RAMBlock is flagged non-migratable. But, when > >>>>> this is done, the RAMBlock has already been cleared from the region, > >>>>> leading to a segv. > >>>>> > >>>>> Fix the issue by testing the RAMBlock before flagging it, as it is > >>>>> done in qemu_ram_unset_idstr() > >>>>> > >>>>> Signed-off-by: Cédric Le Goater <c...@kaod.org> > >>>>> --- > >>>>> > >>>>> I caught this bug while deleting a passthrough device from a pseries > >>>>> machine. Here is the stack: > >>>>> > >>>>> #0 qemu_ram_unset_migratable (rb=0x0) at > >>>>> /home/legoater/work/qemu/qemu-xive-3.0.git/exec.c:1994 > >>>>> #1 0x000000010072def0 in vmstate_unregister_ram (mr=0x101796af0, > >>>>> dev=<optimized out>) > >>>>> #2 0x0000000100694e5c in pci_del_option_rom (pdev=0x101796330) > >>>>> #3 pci_qdev_unrealize (dev=<optimized out>, errp=<optimized out>) > >>>>> #4 0x00000001005ff910 in device_set_realized (obj=0x101796330, > >>>>> value=<optimized out>, errp=0x0) > >>>>> #5 0x00000001007a487c in property_set_bool (obj=0x101796330, > >>>>> v=<optimized out>, name=<optimized out>, > >>>>> #6 0x00000001007a7878 in object_property_set (obj=0x101796330, > >>>>> v=0x7fff70033110, > >>>>> #7 0x00000001007aaf1c in object_property_set_qobject > >>>>> (obj=0x101796330, value=<optimized out>, > >>>>> #8 0x00000001007a7b90 in object_property_set_bool (obj=0x101796330, > >>>>> value=<optimized out>, > >>>>> #9 0x00000001005fcdd8 in device_unparent (obj=0x101796330) > >>>>> #10 0x00000001007a6dd0 in object_finalize_child_property > >>>>> (obj=<optimized out>, name=<optimized out>, > >>>>> #11 0x00000001007a50c0 in object_property_del_child > >>>>> (obj=0x10111f800, child=0x101796330, > >>>>> #12 0x0000000100425cc0 in spapr_phb_remove_pci_device_cb > >>>>> (dev=0x101796330) > >>>>> #13 0x0000000100427974 in spapr_drc_release (drc=0x1017e2df0) > >>>>> #14 0x0000000100429098 in spapr_drc_detach (drc=0x1017e2df0) > >>>>> #15 0x00000001004294e0 in drc_isolate_physical (drc=0x1017e2df0) > >>>>> #16 0x000000010042a50c in rtas_set_isolation_state (state=0, > >>>>> idx=<optimized out>) > >>>>> > >>>>> May be we should call pci_del_option_rom() before > >>>>> pci_unregister_io_regions() ? > >>>> > >>>> This seems to make more sense to me. > >>>> > >>>> Meanwhile I assume the name pci_del_option_rom() is a bit misleading - > >>>> it's not really deleting the ROM but unregistering the ROM only. > >>>> Instead IIUC it's pci_unregister_io_regions() which deleted that. So > >>>> maybe we can either rename the function pci_del_option_rom(), or we > >>>> can pick the ROM destruction out of pci_unregister_io_regions() and > >>>> put it into pci_del_option_rom() to make sure it's done as the last > >>>> step? > >>> > >>> So it is a little more complex than I thought. > >>> > >>> The PCI device is a vfio PCI device and the PCI ROM region is initialized > >>> in vfio_pci_size_rom() with memory_region_init_io(), which does not > >>> allocate the RAMBlock, but has_rom is still set to true. > >>> > >>> When the device is deleted, pci_del_option_rom() is called and with it, > >>> vmstate_unregister_ram() because has_rom is set to true. Leading to the > >>> SEGV. > >>> > >>> I am not sure how to handle this case. It seems that the realize routine > >>> of VFIOPCIDevice is hijacking a little the PCIDevice layer. > >> > >> Indeed. > >> > >> Then now I'm a bit confused on who actually deleted the ROM memory > >> region that was created when pci_add_option_rom() was called. It > >> seems to be leaked. > >> > >> AFAIU the rest of the memory regions of the BARs (0-5) are managed by > >> specific device emulation code, however this ROM memory region is > >> managed by PCI subsystem. Not sure whether that means we should > >> destroy the region in PCI subsystem too, e.g. in pci_del_option_rom(). > >> > >> And now I see this patch might be a valid fix for the VFIO-specific > >> issue (though we might comment that a bit somewhere). > > > > yes. I will send a v2 with an updated commit log. > > I wonder if the fix is simply to... get rid of vmstate_unregister_ram. > > It was added in > > commit b0e56e0b63f350691b52d3e75e89bb64143fbeff > Author: Hu Tao <hu...@cn.fujitsu.com> > Date: Wed Apr 2 15:13:27 2014 +0800 > > unset RAMBlock idstr when unregister MemoryRegion > > Signed-off-by: Hu Tao <hu...@cn.fujitsu.com> > Signed-off-by: Paolo Bonzini <pbonz...@redhat.com> > > whose commit message is a bit lacking, but > http://lists.gnu.org/archive/html/qemu-devel/2014-04/msg00282.html helps > more. It seems like the original bug was a reference count issue. > > Clearing the new migratable flag should also be unnecessary.
But even if we get rid of vmstate_unregister_ram(), the leak could still be there? I'm not sure what was leaked when b0e56e0b6 was introduced, I feel like it's the RAMBlock of the memdev. Here I think the ROM memory region seems to be leaked as well (along with the RAMBlock inside)? Regards, -- Peter Xu
