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?
> >> + 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
>
