On Wed, Sep 01, 2021 at 02:50:42PM +0300, Gal Pressman wrote:
> On 20/08/2021 21:27, Jason Gunthorpe wrote:
> > On Wed, Aug 11, 2021 at 06:11:31PM +0300, Gal Pressman wrote:
> >> diff --git a/drivers/infiniband/hw/efa/efa_main.c b/drivers/infiniband/hw/efa/efa_main.c
> >> index 417dea5f90cf..29db4dec02f0 100644
> >> +++ b/drivers/infiniband/hw/efa/efa_main.c
> >> @@ -67,6 +67,46 @@ static void efa_release_bars(struct efa_dev *dev, int bars_mask)
> >> pci_release_selected_regions(pdev, release_bars);
> >> }
> >>
> >> +static void efa_process_comp_eqe(struct efa_dev *dev, struct efa_admin_eqe *eqe)
> >> +{
> >> + u16 cqn = eqe->u.comp_event.cqn;
> >> + struct efa_cq *cq;
> >> +
> >> + cq = xa_load(&dev->cqs_xa, cqn);
> >> + if (unlikely(!cq)) {
> >
> > This seems unlikely to be correct, what prevents cq from being
> > destroyed concurrently?
> >
> > A comp_handler cannot be running after cq destroy completes.
>
> Sorry for the long turnaround, was OOO.
>
> The CQ cannot be destroyed until all completion events are acked.
> https://github.com/linux-rdma/rdma-core/blob/7fd01f0c6799f0ecb99cae03c22cf7ff61ffbf5a/libibverbs/man/ibv_get_cq_event.3#L45
> https://github.com/linux-rdma/rdma-core/blob/7fd01f0c6799f0ecb99cae03c22cf7ff61ffbf5a/libibverbs/cmd_cq.c#L208
That is something quite different, and in userspace.
What in the kernel prevents tha xa_load and the xa_erase from racing together?
Jason
