[PATCH 5.4 087/453] RDMA/rxe: Compute PSN windows correctly

[Greg Kroah-Hartman]

From: Bob Pearson <rpearsonhpe@xxxxxxxxx>

[ Upstream commit bb3ab2979fd69db23328691cb10067861df89037 ]

The code which limited the number of unacknowledged PSNs was incorrect.
The PSNs are limited to 24 bits and wrap back to zero from 0x00ffffff.
The test was computing a 32 bit value which wraps at 32 bits so that
qp->req.psn can appear smaller than the limit when it is actually larger.

Replace '>' test with psn_compare which is used for other PSN comparisons
and correctly handles the 24 bit size.

Fixes: 8700e3e7c485 ("Soft RoCE driver")
Link: https://lore.kernel.org/r/20201013170741.3590-1-rpearson@xxxxxxx
Signed-off-by: Bob Pearson <rpearson@xxxxxxx>
Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 drivers/infiniband/sw/rxe/rxe_req.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/infiniband/sw/rxe/rxe_req.c b/drivers/infiniband/sw/rxe/rxe_req.c
index e5031172c0193..a4d6e0b7901e9 100644
--- a/drivers/infiniband/sw/rxe/rxe_req.c
+++ b/drivers/infiniband/sw/rxe/rxe_req.c
@@ -664,7 +664,8 @@ next_wqe:
 	}
 
 	if (unlikely(qp_type(qp) == IB_QPT_RC &&
-		     qp->req.psn > (qp->comp.psn + RXE_MAX_UNACKED_PSNS))) {
+		psn_compare(qp->req.psn, (qp->comp.psn +
+				RXE_MAX_UNACKED_PSNS)) > 0)) {
 		qp->req.wait_psn = 1;
 		goto exit;
 	}
-- 
2.27.0