On 2/13/2024 11:10 AM, Eugenio Perez Martin wrote:

On Mon, Feb 12, 2024 at 6:16 PM Steve Sistare [off-list ref] wrote:

quoted

Flush to guarantee no workers are running when suspend returns.

Signed-off-by: Steve Sistare <redacted>
---
 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?

quoted

+       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