Re: [PATCH for-next 4/4] RDMA/efa: CQ notifications

[Gal Pressman <galpress@amazon.com>]

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

>> @@ -421,6 +551,7 @@ static struct efa_dev *efa_probe_device(struct pci_dev *pdev)
>>  	edev->efa_dev = dev;
>>  	edev->dmadev = &pdev->dev;
>>  	dev->pdev = pdev;
>> +	xa_init_flags(&dev->cqs_xa, XA_FLAGS_LOCK_IRQ);
> 
> And this is confusing too, since the above is the only reference and
> doesn't take the xa_lock why does the xa need to use LOCK_IRQ?

Oh, I'm now noticing that the load operation uses an rcu lock, not the xa_lock..
This can be replaced with xa_init().

Thanks for the review.