Re: [Qemu-devel] [PATCH 2/5] exec.c: use refcnt to protect device during dispatching

[liu ping fan]

On Wed, Jul 25, 2012 at 3:43 PM, Stefan Hajnoczi <address@hidden> wrote:
> On Wed, Jul 25, 2012 at 4:31 AM, Liu Ping Fan <address@hidden> wrote:
>> @@ -3396,13 +3420,25 @@ void cpu_physical_memory_rw(target_phys_addr_t addr, 
>> uint8_t *buf,
>>      uint32_t val;
>>      target_phys_addr_t page;
>>      MemoryRegionSection *section;
>> +    Object *bk;
>>
>>      while (len > 0) {
>>          page = addr & TARGET_PAGE_MASK;
>>          l = (page + TARGET_PAGE_SIZE) - addr;
>>          if (l > len)
>>              l = len;
>> +
>> +        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?
Thanx, pingfan
> another patch to perform atomic increment/decrement or how will
> per-device synchronization work?
>
> Stefan