Re: [Qemu-devel] [PATCH 15/16] tcg: Make tb_flush() thread safe

[Paolo Bonzini]

On 21/09/2016 19:37, Emilio G. Cota wrote:
> On Wed, Sep 21, 2016 at 18:19:26 +0200, Paolo Bonzini wrote:
>>
>>
>> On 21/09/2016 18:05, Emilio G. Cota wrote:
>>>>> +    tb_lock();
>>>>> +
>>>>> +    /* If it's already been done on request of another CPU,
>>>>> +     * just retry.
>>>>> +     */
>>>>> +    if (atomic_read(&tcg_ctx.tb_ctx.tb_flush_count) != tb_flush_req) {
>>>>> +        goto done;
>>> tb_flush_count is always accessed with tb_lock held, right? If so, I don't
>>> see a reason to access it with atomic_read/set.
>>
>> tb_flush accesses it outside tb_lock.  Technically this one you're
>> quoting need not use atomic_read, but others need to.
> 
> Sorry for being thick, but when does tb_flush not own tb_lock?
> (I'm assuming we're talking only user-mode, since full-system has
> for now empty tb_lock/unlock helpers.)

When called from gdbstub I think it doesn't (and for system-mode in
other cases too, so better be ready anyway).

Paolo