Re: [Qemu-devel] [PATCH] linux-user: Fix do_store_exclusive for shared memory of interprocess.

[Richard Henderson]

On 10/15/2016 08:53 AM, Heiher wrote:
> +    if ((__hptr = lock_user(VERIFY_WRITE, __gaddr, sizeof(target_type), 0))) { 
> \
> +        if ((old) != atomic_cmpxchg(__hptr, (old), (new)))             \
> +            __ret = -TARGET_EAGAIN;                                    \
> +        unlock_user(__hptr, __gaddr, sizeof(target_type));             \

This doesn't perform an atomic operation, because lock_user and unlock_user 
copy data from and to the guest.  The atomic operation you're doing is on 
memory private to the host.

You also have to handle host byte order != target byte order.

That said, we are some way toward addressing this.  The patch set that Emilio 
pointed you at is a good start.


r~