[Qemu-devel] [PATCH] exec.c: check RAMBlock validity before changing its flag

["Cédric Le Goater" <clg@kaod.org>]

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 <clg@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() ?

 exec.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/exec.c b/exec.c
index ebadc0e302ad..0dabf7380438 100644
--- a/exec.c
+++ b/exec.c
@@ -1992,7 +1992,9 @@ void qemu_ram_set_migratable(RAMBlock *rb)
 
 void qemu_ram_unset_migratable(RAMBlock *rb)
 {
-    rb->flags &= ~RAM_MIGRATABLE;
+    if (rb) {
+        rb->flags &= ~RAM_MIGRATABLE;
+    }
 }
 
 /* Called with iothread lock held.  */
-- 
2.13.6