On Fri, Jan 30, 2026 at 3:56 PM Eugenio Perez Martin <[email protected]> wrote: > > On Fri, Jan 30, 2026 at 3:18 AM Jason Wang <[email protected]> wrote: > > > > On Thu, Jan 29, 2026 at 2:21 PM Eugenio Perez Martin > > <[email protected]> wrote: > > > > > > On Thu, Jan 29, 2026 at 2:17 AM Jason Wang <[email protected]> wrote: > > > > > > > > On Wed, Jan 28, 2026 at 8:45 PM Eugenio Pérez <[email protected]> > > > > wrote: > > > > > > > > > > The vduse_vdpa_set_vq_ready can be called in the lifetime of the > > > > > device > > > > > well after initial setup, and the device can read it afterwards. > > > > > > > > > > Ensure that reads and writes to vq->ready are SMP safe so that the > > > > > caller can trust that virtqueue kicks and calls behave as expected > > > > > immediately after the operation returns. > > > > > > > > > > Signed-off-by: Eugenio Pérez <[email protected]> > > > > > --- > > > > > drivers/vdpa/vdpa_user/vduse_dev.c | 34 > > > > > +++++++++++++++++++++++------- > > > > > 1 file changed, 26 insertions(+), 8 deletions(-) > > > > > > > > > > diff --git a/drivers/vdpa/vdpa_user/vduse_dev.c > > > > > b/drivers/vdpa/vdpa_user/vduse_dev.c > > > > > index 73d1d517dc6c..a4963aaf9332 100644 > > > > > --- a/drivers/vdpa/vdpa_user/vduse_dev.c > > > > > +++ b/drivers/vdpa/vdpa_user/vduse_dev.c > > > > > @@ -460,6 +460,24 @@ static __poll_t vduse_dev_poll(struct file > > > > > *file, poll_table *wait) > > > > > return mask; > > > > > } > > > > > > > > > > +static bool vduse_vq_get_ready(const struct vduse_virtqueue *vq) > > > > > +{ > > > > > + /* > > > > > + * Paired with vduse_vq_set_ready smp_store, as the driver > > > > > may modify > > > > > + * it while the VDUSE instance is reading it. > > > > > + */ > > > > > + return smp_load_acquire(&vq->ready); > > > > > +} > > > > > + > > > > > +static void vduse_vq_set_ready(struct vduse_virtqueue *vq, bool > > > > > ready) > > > > > +{ > > > > > + /* > > > > > + * Paired with vduse_vq_get_ready smp_load, as the driver may > > > > > modify > > > > > + * it while the VDUSE instance is reading it. > > > > > + */ > > > > > + smp_store_release(&vq->ready, ready); > > > > > > > > Assuming this is not used in the datapath, I wonder if we can simply > > > > use vq_lock mutex. > > > > > > > > > > The function vduse_vq_set/get_ready are not in the datapath, but > > > vduse_vq_kick and vduse_vq_signal_irqfd are. I'm ok if you want to > > > switch to vq_mutex if you want though, maybe it's even comparable with > > > the cost of the ioctls or eventfd signaling. > > > > I'd like to use mutex for simplicity. > > > > I cannot move it to a mutex, as we need to take it in the critical > sections of the kick_lock and irq_lock spinlocks. > > I can move it to a spinlock, but it seems more complicated to me. We > need to make sure we always take these kick_lock and irq_lock in the > same order as the ready_lock, to not create deadlocks, and they always > protect just the ready boolean. But sure, I'll send the spinlock > version for V2.
Thinking about this, I'm not sure I understand the issue. Maybe you can give me an example of the race. THanks >
