On 02/09/2021 16:02, Jason Gunthorpe wrote:

On Thu, Sep 02, 2021 at 10:03:16AM +0300, Gal Pressman wrote:

quoted

On 01/09/2021 18:36, Jason Gunthorpe wrote:

quoted

On Wed, Sep 01, 2021 at 05:24:43PM +0300, Gal Pressman wrote:

quoted

On 01/09/2021 14:57, Jason Gunthorpe wrote:

quoted

On Wed, Sep 01, 2021 at 02:50:42PM +0300, Gal Pressman wrote:

quoted

On 20/08/2021 21:27, Jason Gunthorpe wrote:

quoted

On Wed, Aug 11, 2021 at 06:11:31PM +0300, Gal Pressman wrote:

quoted

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

Oh nice, thanks.

I think the code would be much simpler using synchronize_rcu(), and the
destroy_cq flow is usually on the cold path anyway. I also prefer to be certain
that the CQ is freed once the destroy verb returns and not rely on the callback
scheduling.