[PATCH for-next] RDMA/rxe: Fix ref count error in check_rkey()

[Bob Pearson <rpearsonhpe@gmail.com>]

There is a reference count error in error path code and a
potential race in check_rkey() in rxe_resp.c. When looking
up the rkey for a memory window the reference to the mw from
rxe_lookup_mw() is dropped before a reference is taken on the
mr referenced by the mw. If the mr is destroyed immediately
after the call to rxe_put(mw) the mr pointer is unprotected
and may end up pointing at freed memory. The rxe_get(mr) call
should take place before the rxe_put(mw) call.

All errors in check_rkey() call rxe_put(mw) if mw is not NULL
but it was already called after the above. The mw pointer
should be set to NULL after the rxe_put(mw) call to prevent
this from happening.

This patch corrects these errors.

Fixes: cdd0b85675ae ("RDMA/rxe: Implement memory access through MWs")
Signed-off-by: Bob Pearson <rpearsonhpe@gmail.com>
---
 drivers/infiniband/sw/rxe/rxe_resp.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/infiniband/sw/rxe/rxe_resp.c b/drivers/infiniband/sw/rxe/rxe_resp.c
index 68f6cd188d8e..5d8d336c402d 100644
--- a/drivers/infiniband/sw/rxe/rxe_resp.c
+++ b/drivers/infiniband/sw/rxe/rxe_resp.c
@@ -489,8 +489,9 @@ static enum resp_states check_rkey(struct rxe_qp *qp,
 		if (mw->access & IB_ZERO_BASED)
 			qp->resp.offset = mw->addr;
 
-		rxe_put(mw);
 		rxe_get(mr);
+		rxe_put(mw);
+		mw = NULL;
 	} else {
 		mr = lookup_mr(qp->pd, access, rkey, RXE_LOOKUP_REMOTE);
 		if (!mr) {
-- 
2.37.2