Il 29/07/2013 10:10, liu ping fan ha scritto:
> On Mon, Jul 29, 2013 at 2:30 PM, Paolo Bonzini <pbonz...@redhat.com> wrote:
>> Il 29/07/2013 05:16, Liu Ping Fan ha scritto:
>>> After disabling the QemuClock, we should make sure that no QemuTimers
>>> are still in flight. To implement that, the caller of disabling will
>>> wait until the last user's exit.
>>>
>>> Note, the callers of qemu_clock_enable() should be sync by themselves,
>>> not protected by this patch.
>>>
>>> Signed-off-by: Liu Ping Fan <pingf...@linux.vnet.ibm.com>
>>
>> This is an interesting approach.
>>
>>> - if (!clock->enabled)
>>> - return;
>>> + atomic_inc(&clock->using);
>>> + if (unlikely(!clock->enabled)) {
>>> + goto exit;
>>> + }
>>
>> This can return directly, it doesn't need to increment and decrement
>> clock->using.
>>
> Here is a race condition like the following
Ah, I see.
Still this seems a bit backwards. Most of the time you will have no one
on the wait_using condvar, but you are almost always signaling the
condvar (should be broadcast BTW)...
Paolo
