On Wed, Jul 25, 2012 at 5:18 PM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
> Il 25/07/2012 10:12, liu ping fan ha scritto:
>>>> >> + qemu_rwlock_rdlock_devtree();
>>>> >> section = phys_page_find(page >> TARGET_PAGE_BITS);
>>>> >> + if (!(memory_region_is_ram(section->mr) ||
>>>> >> + memory_region_is_romd(section->mr)) && !is_write) {
>>>> >> + bk = get_backend(section->mr, addr);
>>>> >> + object_ref(bk);
>>>> >> + } else if (!memory_region_is_ram(section->mr) && is_write) {
>>>> >> + bk = get_backend(section->mr, addr);
>>>> >> + object_ref(bk);
>>>> >> + }
>>>> >> + qemu_rwlock_unlock_devtree();
>>>> >>
>>>> >> if (is_write) {
>>>> >> if (!memory_region_is_ram(section->mr)) {
>>>> >> @@ -3426,6 +3462,7 @@ void cpu_physical_memory_rw(target_phys_addr_t addr, uint8_t *buf,
>>>> >> io_mem_write(section->mr, addr1, val, 1);
>>>> >> l = 1;
>>>> >> }
>>>> >> + object_unref(bk);
>>> >
>>> > Currently object_ref()/object_unref() are not atomic. Will you send
>> We obey the rule:
>> rdlock->search->ref_get,
>> wrlock->remove ->ref_put
>> So can it causes problem if object_ref()/object_unref() are not atomic?
>
> Yes, two CPUs can perform object_ref at the same time.
>
> You can find a header file for atomic operations here:
> https://github.com/bonzini/qemu/commit/atomics.patch
>
Got it, thanks
> Paolo
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