[PATCH v3 1/1] Fix the coredump when memory backend id conflicts with default_ram_id

[Li Zhang]

When no memory backend is specified in machine options,
a default memory device will be added with default_ram_id.
However, if a memory backend object is added in QEMU options
and id is the same as default_ram_id, a coredump happens.

Command line:
qemu-system-x86_64 -name guest=vmtest,debug-threads=on \
-machine pc-q35-6.0,accel=kvm,usb=off,vmport=off \
-smp 16,sockets=16,cores=1,threads=1 \
-m 4G \
-object memory-backend-ram,id=pc.ram,size=4G \
-no-user-config -nodefaults -nographic

Stack trace of thread 16903:
    #0  0x00007fb109a9318b raise (libc.so.6 + 0x3a18b)
    #1  0x00007fb109a94585 abort (libc.so.6 + 0x3b585)
    #2  0x0000558c34bc89be error_handle_fatal (qemu-system-x86_64 + 0x9c89be)
    #3  0x0000558c34bc8aee error_setv (qemu-system-x86_64 + 0x9c8aee)
    #4  0x0000558c34bc8ccf error_setg_internal (qemu-system-x86_64 + 0x9c8ccf)
    #5  0x0000558c349f6899 object_property_try_add (qemu-system-x86_64 + 
0x7f6899)
    #6  0x0000558c349f7df8 object_property_try_add_child (qemu-system-x86_64 + 
0x7f7df8)
    #7  0x0000558c349f7e91 object_property_add_child (qemu-system-x86_64 + 
0x7f7e91)
    #8  0x0000558c3454686d create_default_memdev (qemu-system-x86_64 + 0x34686d)
    #9  0x0000558c34546f58 qemu_init_board (qemu-system-x86_64 + 0x346f58)
    #10 0x0000558c345471b9 qmp_x_exit_preconfig (qemu-system-x86_64 + 0x3471b9)
    #11 0x0000558c345497d9 qemu_init (qemu-system-x86_64 + 0x3497d9)
    #12 0x0000558c344e54c2 main (qemu-system-x86_64 + 0x2e54c2)
    #13 0x00007fb109a7e34d __libc_start_main (libc.so.6 + 0x2534d)
    #14 0x0000558c344e53ba _start (qemu-system-x86_64 + 0x2e53ba)

Signed-off-by: Li Zhang <lizh...@suse.de>
---
 hw/core/machine.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/hw/core/machine.c b/hw/core/machine.c
index a673302cce..9ede63b01c 100644
--- a/hw/core/machine.c
+++ b/hw/core/machine.c
@@ -1265,9 +1265,21 @@ MemoryRegion *machine_consume_memdev(MachineState 
*machine,
 static bool create_default_memdev(MachineState *ms, const char *path, Error 
**errp)
 {
     Object *obj;
+    ObjectProperty *prop;
     MachineClass *mc = MACHINE_GET_CLASS(ms);
     bool r = false;
 
+    prop = object_property_find(object_get_objects_root(), mc->default_ram_id);
+    if (prop) {
+        error_report("A memory backend with id '%s' already exists, "
+                     "cannot create default RAM backend with the same id. "
+                     "Either change id of the offending backend or "
+                     "provide system RAM backend explicitly using "
+                     "'-machine memory-backend' option. " ,
+                     mc->default_ram_id);
+        exit(EXIT_FAILURE);
+    }
+
     obj = object_new(path ? TYPE_MEMORY_BACKEND_FILE : 
TYPE_MEMORY_BACKEND_RAM);
     if (path) {
         if (!object_property_set_str(obj, "mem-path", path, errp)) {
-- 
2.34.1