staging/rdma/hfi1: Fix bug that could block the process on context exit

A race was discovred in the user SDMA code, which could result
in an process being stuck in the kernel call indefinitely in
certain error conditions.

If, during the processing of a user SDMA request, there was an
error *and* all outstanding SDMA descriptor had been completed
by the time the that error case was handled in the calling function,
the state of the packet queue would not get correctly updated
resulting in the process subsequently getting stuck, thinking that
there are more descriptors to be completed.

To handle this scenario, the driver now checks the submitted
packet count vs. the completed. If all submitted packets have also
been completed, the driver can safely free the request and signal
user level. Otherwise, this will be handled by the completion
callback.
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Mitko Haralanov <mitko.haralanov@intel.com>
Signed-off-by: Jubin John <jubin.john@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/staging/rdma/hfi1/user_sdma.c

@@ -678,7 +678,6 @@ int hfi1_user_sdma_process_request(struct file *fp, struct iovec *iovec,
 	ret = user_sdma_send_pkts(req, pcount);
 	if (unlikely(ret < 0 && ret != -EBUSY)) {
 		req->status = ret;
-		atomic_dec(&pq->n_reqs);
 		goto free_req;
 	}
 
@@ -703,6 +702,9 @@ int hfi1_user_sdma_process_request(struct file *fp, struct iovec *iovec,
 			if (ret != -EBUSY) {
 				req->status = ret;
 				set_bit(SDMA_REQ_DONE_ERROR, &req->flags);
+				if (ACCESS_ONCE(req->seqcomp) ==
+				    req->seqsubmitted - 1)
+					goto free_req;
 				return ret;
 			}
 			wait_event_interruptible_timeout(
@@ -717,6 +719,7 @@ int hfi1_user_sdma_process_request(struct file *fp, struct iovec *iovec,
 	return 0;
 free_req:
 	user_sdma_free_request(req, true);
+	pq_update(pq);
 	set_comp_state(pq, cq, info.comp_idx, ERROR, req->status);
 	return ret;
 }