Subject: RE: [EXTERNAL] Re: [Patch v7 5/5] RDMA/mana_ib: Send event to qp

quoted

-----Original Message-----
From: Jason Gunthorpe <jgg@ziepe.ca>
Sent: Monday, October 23, 2023 11:24 AM
To: sharmaajay@linuxonhyperv.com
Cc: Long Li <longli@microsoft.com>; Leon Romanovsky <leon@kernel.org>;
Dexuan Cui [off-list ref]; Wei Liu [off-list ref]; David S.
Miller [off-list ref]; Eric Dumazet [off-list ref];
Jakub Kicinski [off-list ref]; Paolo Abeni [off-list ref];
linux- rdma@vger.kernel.org; linux-hyperv@vger.kernel.org;
netdev@vger.kernel.org; linux-kernel@vger.kernel.org; Ajay Sharma
[off-list ref]
Subject: [EXTERNAL] Re: [Patch v7 5/5] RDMA/mana_ib: Send event to qp

On Mon, Oct 16, 2023 at 03:12:02PM -0700,

sharmaajay@linuxonhyperv.com

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wrote:

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diff --git a/drivers/infiniband/hw/mana/qp.c

b/drivers/infiniband/hw/mana/qp.c index ef3275ac92a0..19fae28985c3
100644

--- a/drivers/infiniband/hw/mana/qp.c
+++ b/drivers/infiniband/hw/mana/qp.c

@@ -210,6 +210,8 @@ static int mana_ib_create_qp_rss(struct ib_qp

*ibqp, struct ib_pd *pd,

quoted

 		wq->id = wq_spec.queue_index;
 		cq->id = cq_spec.queue_index;

+		xa_store(&mib_dev->rq_to_qp_lookup_table, wq->id, qp,

GFP_KERNEL);

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+

A store with no erase?

A load with no locking?

This can't be right

Jason

This wq->id is assigned from the HW and is guaranteed to be unique. May be I
am not following why do we need a lock here. Can you please explain ?
Ajay

I think we need to check the return value of xa_store(), and call xa_erase() in mana_ib_destroy_qp().

wq->id is generated by the hardware. If we believe in hardware always behaves in good manner, we don't need a lock.

Thanks,

Long