答复: [PATCH V8 6/8] physmem: Add helper function to destroy CPU AddressSpace

[zhukeqian via]

Hi Salil,

[...]

+void cpu_address_space_destroy(CPUState *cpu, int asidx) {
+    CPUAddressSpace *cpuas;
+
+    assert(cpu->cpu_ases);
+    assert(asidx >= 0 && asidx < cpu->num_ases);
+    /* KVM cannot currently support multiple address spaces. */
+    assert(asidx == 0 || !kvm_enabled());
+
+    cpuas = &cpu->cpu_ases[asidx];
+    if (tcg_enabled()) {
+        memory_listener_unregister(&cpuas->tcg_as_listener);
+    }
+
+    address_space_destroy(cpuas->as);
+    g_free_rcu(cpuas->as, rcu);

In address_space_destroy(), it calls call_rcu1() on cpuas->as which will set 
do_address_space_destroy() as the rcu func.
And g_free_rcu() also calls call_rcu1() on cpuas->as which will overwrite the 
rcu func as g_free().

Then I think the g_free() may be called twice in rcu thread, please verify that.

The source code of call_rcu1:

void call_rcu1(struct rcu_head *node, void (*func)(struct rcu_head *node))
{
    node->func = func;
    enqueue(node);
    qatomic_inc(&rcu_call_count);
    qemu_event_set(&rcu_call_ready_event);
}

Thanks,
Keqian

+
+    if (asidx == 0) {
+        /* reset the convenience alias for address space 0 */
+        cpu->as = NULL;
+    }
+
+    if (--cpu->cpu_ases_count == 0) {
+        g_free(cpu->cpu_ases);
+        cpu->cpu_ases = NULL;
+    }
+}
+
 AddressSpace *cpu_get_address_space(CPUState *cpu, int asidx)  {
     /* Return the AddressSpace corresponding to the specified index */
--
2.34.1