[PATCH] qat: fix deadlock in backlog processing

I was testing QAT with dm-crypt and I got some deadlocks.

The reason for the deadlocks is this: suppose that one of the "if"
conditions in "qat_alg_send_message_maybacklog" is true and we jump to the
"enqueue" label. At this point, an interrupt comes in and clears all
pending messages. Now, the interrupt returns, we grab backlog->lock, add
the message to the backlog, drop backlog->lock - and there is no one to
remove the backlogged message out of the list and submit it.

I fixed it with this patch. I didn't want to add a spinlock to the hot
path, so I take it only if some of the condition suggests that queuing may
be required.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Cc: stable@vger.kernel.org

---
 drivers/crypto/intel/qat/qat_common/qat_algs_send.c |   45 +++++++++++---------
 1 file changed, 25 insertions(+), 20 deletions(-)

Index: linux-2.6/drivers/crypto/intel/qat/qat_common/qat_algs_send.c
===================================================================
--- linux-2.6.orig/drivers/crypto/intel/qat/qat_common/qat_algs_send.c
+++ linux-2.6/drivers/crypto/intel/qat/qat_common/qat_algs_send.c
@@ -40,39 +40,44 @@ void qat_alg_send_backlog(struct qat_ins
 	spin_unlock_bh(&backlog->lock);
 }
 
-static void qat_alg_backlog_req(struct qat_alg_req *req,
-				struct qat_instance_backlog *backlog)
-{
-	INIT_LIST_HEAD(&req->list);
-
-	spin_lock_bh(&backlog->lock);
-	list_add_tail(&req->list, &backlog->list);
-	spin_unlock_bh(&backlog->lock);
-}
-
-static int qat_alg_send_message_maybacklog(struct qat_alg_req *req)
+static bool qat_alg_try_to_send(struct qat_alg_req *req)
 {
 	struct qat_instance_backlog *backlog = req->backlog;
 	struct adf_etr_ring_data *tx_ring = req->tx_ring;
 	u32 *fw_req = req->fw_req;
 
 	/* If any request is already backlogged, then add to backlog list */
-	if (!list_empty(&backlog->list))
-		goto enqueue;
+	if (unlikely(!list_empty(&backlog->list)))
+		return false;
 
 	/* If ring is nearly full, then add to backlog list */
-	if (adf_ring_nearly_full(tx_ring))
-		goto enqueue;
+	if (unlikely(adf_ring_nearly_full(tx_ring)))
+		return false;
 
 	/* If adding request to HW ring fails, then add to backlog list */
-	if (adf_send_message(tx_ring, fw_req))
-		goto enqueue;
+	if (unlikely(adf_send_message(tx_ring, fw_req)))
+		return false;
 
-	return -EINPROGRESS;
+	return true;
+}
 
-enqueue:
-	qat_alg_backlog_req(req, backlog);
+static int qat_alg_send_message_maybacklog(struct qat_alg_req *req)
+{
+	struct qat_instance_backlog *backlog = req->backlog;
+
+	if (likely(qat_alg_try_to_send(req)))
+		return -EINPROGRESS;
+
+	spin_lock_bh(&backlog->lock);
 
+	if (unlikely(qat_alg_try_to_send(req))) {
+		spin_unlock_bh(&backlog->lock);
+		return -EINPROGRESS;
+	}
+
+	list_add_tail(&req->list, &backlog->list);
+
+	spin_unlock_bh(&backlog->lock);
 	return -EBUSY;
 }