On Thu, Sep 02, 2021 at 10:03:16AM +0300, Gal Pressman wrote:
> On 01/09/2021 18:36, Jason Gunthorpe wrote:
> > On Wed, Sep 01, 2021 at 05:24:43PM +0300, Gal Pressman wrote:
> >> On 01/09/2021 14:57, Jason Gunthorpe wrote:
> >>> 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?
> >>
> >> Good point.
> >> I think we need to surround efa_process_comp_eqe() with an rcu_read_lock() and
> >> have a synchronize_rcu() after removing it from the xarray in
> >> destroy_cq.
> >
> > Try to avoid synchronize_rcu()
>
> I don't see how that's possible?
Usually people use call_rcu() instead
> Sure, I wasn't sure if it's OK to nest rcu_read_lock() calls.
It is OK
Jason
