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

[Stefan Hajnoczi]

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
another patch to perform atomic increment/decrement or how will
per-device synchronization work?

Stefan