On 2/14/2024 2:39 PM, Eugenio Perez Martin wrote:
> On Wed, Feb 14, 2024 at 6:50 PM Steven Sistare
> <steven.sistare@xxxxxxxxxx> wrote:
>>
>> On 2/13/2024 11:10 AM, Eugenio Perez Martin wrote:
>>> On Mon, Feb 12, 2024 at 6:16 PM Steve Sistare <steven.sistare@xxxxxxxxxx> wrote:
>>>>
>>>> Flush to guarantee no workers are running when suspend returns.
>>>>
>>>> Signed-off-by: Steve Sistare <steven.sistare@xxxxxxxxxx>
>>>> ---
>>>> drivers/vdpa/vdpa_sim/vdpa_sim.c | 13 +++++++++++++
>>>> 1 file changed, 13 insertions(+)
>>>>
>>>> diff --git a/drivers/vdpa/vdpa_sim/vdpa_sim.c b/drivers/vdpa/vdpa_sim/vdpa_sim.c
>>>> index be2925d0d283..a662b90357c3 100644
>>>> --- a/drivers/vdpa/vdpa_sim/vdpa_sim.c
>>>> +++ b/drivers/vdpa/vdpa_sim/vdpa_sim.c
>>>> @@ -74,6 +74,17 @@ static void vdpasim_worker_change_mm_sync(struct vdpasim *vdpasim,
>>>> kthread_flush_work(work);
>>>> }
>>>>
>>>> +static void flush_work_fn(struct kthread_work *work) {}
>>>> +
>>>> +static void vdpasim_flush_work(struct vdpasim *vdpasim)
>>>> +{
>>>> + struct kthread_work work;
>>>> +
>>>> + kthread_init_work(&work, flush_work_fn);
>>>
>>> If the work is already queued, doesn't it break the linked list
>>> because of the memset in kthread_init_work?
>>
>> work is a local variable. It completes before vdpasim_flush_work returns,
>> thus is never already queued on entry to vdpasim_flush_work.
>> Am I missing your point?
>
> No, sorry, I was the one missing that. Thanks for explaining it :)!
>
> I'm not so used to the kthread queue, but why not calling
> kthread_flush_work on vdpasim->work directly?
vdpasim->work is not the only work posted to vdpasim->worker; see
vdpasim_worker_change_mm_sync. Posting a new no-op work guarantees
they are all flushed.
- Steve
>>>> + kthread_queue_work(vdpasim->worker, &work);
>>>> + kthread_flush_work(&work);
>>>> +}
>>>> +
>>>> static struct vdpasim *vdpa_to_sim(struct vdpa_device *vdpa)
>>>> {
>>>> return container_of(vdpa, struct vdpasim, vdpa);
>>>> @@ -511,6 +522,8 @@ static int vdpasim_suspend(struct vdpa_device *vdpa)
>>>> vdpasim->running = false;
>>>> mutex_unlock(&vdpasim->mutex);
>>>>
>>>> + vdpasim_flush_work(vdpasim);
>>>
>>> Do we need to protect the case where vdpasim_kick_vq and
>>> vdpasim_suspend are called "at the same time"? Correct userland should
>>> not be doing it but buggy or mailious could be. Just calling
>>> vdpasim_flush_work with the mutex acquired would solve the issue,
>>> doesn't it?
>>
>> Good catch. I need to serialize access to vdpasim->running plus the worker queue
>> in these two functions. vdpasim_kick_vq currently takes no locks. In case it is called
>> from non-task contexts, I should define a new spinlock to be acquired in both functions.
>>
>> - Steve
>>
>
