RE: [PATCH 5/5] IB/hfi1: Fix improper uses of smp_mb__before_atomic()

[Ruhl, Michael J]

>-----Original Message-----
>From: linux-rdma-owner@xxxxxxxxxxxxxxx [mailto:linux-rdma-
>owner@xxxxxxxxxxxxxxx] On Behalf Of Andrea Parri
>Sent: Monday, April 29, 2019 4:15 PM
>To: linux-kernel@xxxxxxxxxxxxxxx
>Cc: Andrea Parri <andrea.parri@xxxxxxxxxxxxxxxxxxxx>;
>stable@xxxxxxxxxxxxxxx; Dalessandro, Dennis
><dennis.dalessandro@xxxxxxxxx>; Marciniszyn, Mike
><mike.marciniszyn@xxxxxxxxx>; Doug Ledford <dledford@xxxxxxxxxx>;
>Jason Gunthorpe <jgg@xxxxxxxx>; linux-rdma@xxxxxxxxxxxxxxx
>Subject: [PATCH 5/5] IB/hfi1: Fix improper uses of smp_mb__before_atomic()
>
>This barrier only applies to the read-modify-write operations; in
>particular, it does not apply to the atomic_read() primitive.
>
>Replace the barrier with an smp_mb().

This is one of a couple of barrier issues that we are currently looking into.

See:

[PATCH for-next 6/9] IB/rdmavt: Add new completion inline

We will take a look at this one as well.

Thanks,

Mike

>Fixes: 856cc4c237add ("IB/hfi1: Add the capability for reserved operations")
>Cc: stable@xxxxxxxxxxxxxxx
>Reported-by: "Paul E. McKenney" <paulmck@xxxxxxxxxxxxx>
>Reported-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
>Signed-off-by: Andrea Parri <andrea.parri@xxxxxxxxxxxxxxxxxxxx>
>Cc: Dennis Dalessandro <dennis.dalessandro@xxxxxxxxx>
>Cc: Mike Marciniszyn <mike.marciniszyn@xxxxxxxxx>
>Cc: Doug Ledford <dledford@xxxxxxxxxx>
>Cc: Jason Gunthorpe <jgg@xxxxxxxx>
>Cc: linux-rdma@xxxxxxxxxxxxxxx
>---
> drivers/infiniband/sw/rdmavt/qp.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
>diff --git a/drivers/infiniband/sw/rdmavt/qp.c
>b/drivers/infiniband/sw/rdmavt/qp.c
>index a34b9a2a32b60..b64fd151d31fb 100644
>--- a/drivers/infiniband/sw/rdmavt/qp.c
>+++ b/drivers/infiniband/sw/rdmavt/qp.c
>@@ -1863,11 +1863,11 @@ static inline int rvt_qp_is_avail(
> 	u32 reserved_used;
>
> 	/* see rvt_qp_wqe_unreserve() */
>-	smp_mb__before_atomic();
>+	smp_mb();
> 	reserved_used = atomic_read(&qp->s_reserved_used);
> 	if (unlikely(reserved_op)) {
> 		/* see rvt_qp_wqe_unreserve() */
>-		smp_mb__before_atomic();
>+		smp_mb();
> 		if (reserved_used >= rdi->dparms.reserved_operations)
> 			return -ENOMEM;
> 		return 0;
>@@ -1882,7 +1882,7 @@ static inline int rvt_qp_is_avail(
> 		avail = slast - qp->s_head;
>
> 	/* see rvt_qp_wqe_unreserve() */
>-	smp_mb__before_atomic();
>+	smp_mb();
> 	reserved_used = atomic_read(&qp->s_reserved_used);
> 	avail =  avail - 1 -
> 		(rdi->dparms.reserved_operations - reserved_used);
>--
>2.7.4