IB/hfi1: Remove race conditions in user_sdma send path

Packet queue state is over used to determine SDMA descriptor
availablitity and packet queue request state.

cpu 0  ret = user_sdma_send_pkts(req, pcount);
cpu 0  if (atomic_read(&pq->n_reqs))
cpu 1  IRQ user_sdma_txreq_cb calls pq_update() (state to _INACTIVE)
cpu 0        xchg(&pq->state, SDMA_PKT_Q_ACTIVE);

At this point pq->n_reqs == 0 and pq->state is incorrectly
SDMA_PKT_Q_ACTIVE.  The close path will hang waiting for the state
to return to _INACTIVE.

This can also change the state from _DEFERRED to _ACTIVE.  However,
this is a mostly benign race.

Remove the racy code path.

Use n_reqs to determine if a packet queue is active or not.

Reviewed-by: Mitko Haralanov <mitko.haralanov@intel.com>
Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/hfi1/user_sdma.c

@@ -187,7 +187,6 @@ int hfi1_user_sdma_alloc_queues(struct hfi1_ctxtdata *uctxt,
 	pq->ctxt = uctxt->ctxt;
 	pq->subctxt = fd->subctxt;
 	pq->n_max_reqs = hfi1_sdma_comp_ring_size;
-	pq->state = SDMA_PKT_Q_INACTIVE;
 	atomic_set(&pq->n_reqs, 0);
 	init_waitqueue_head(&pq->wait);
 	atomic_set(&pq->n_locked, 0);
@@ -276,7 +275,7 @@ int hfi1_user_sdma_free_queues(struct hfi1_filedata *fd,
 		/* Wait until all requests have been freed. */
 		wait_event_interruptible(
 			pq->wait,
-			(READ_ONCE(pq->state) == SDMA_PKT_Q_INACTIVE));
+			!atomic_read(&pq->n_reqs));
 		kfree(pq->reqs);
 		kfree(pq->req_in_use);
 		kmem_cache_destroy(pq->txreq_cache);
@@ -312,6 +311,13 @@ static u8 dlid_to_selector(u16 dlid)
 	return mapping[hash];
 }
 
+/**
+ * hfi1_user_sdma_process_request() - Process and start a user sdma request
+ * @fd: valid file descriptor
+ * @iovec: array of io vectors to process
+ * @dim: overall iovec array size
+ * @count: number of io vector array entries processed
+ */
 int hfi1_user_sdma_process_request(struct hfi1_filedata *fd,
 				   struct iovec *iovec, unsigned long dim,
 				   unsigned long *count)
@@ -560,20 +566,12 @@ int hfi1_user_sdma_process_request(struct hfi1_filedata *fd,
 		req->ahg_idx = sdma_ahg_alloc(req->sde);
 
 	set_comp_state(pq, cq, info.comp_idx, QUEUED, 0);
+	pq->state = SDMA_PKT_Q_ACTIVE;
 	/* Send the first N packets in the request to buy us some time */
 	ret = user_sdma_send_pkts(req, pcount);
 	if (unlikely(ret < 0 && ret != -EBUSY))
 		goto free_req;
 
-	/*
-	 * It is possible that the SDMA engine would have processed all the
-	 * submitted packets by the time we get here. Therefore, only set
-	 * packet queue state to ACTIVE if there are still uncompleted
-	 * requests.
-	 */
-	if (atomic_read(&pq->n_reqs))
-		xchg(&pq->state, SDMA_PKT_Q_ACTIVE);
-
 	/*
 	 * This is a somewhat blocking send implementation.
 	 * The driver will block the caller until all packets of the
@@ -1409,10 +1407,8 @@ static void user_sdma_txreq_cb(struct sdma_txreq *txreq, int status)
 
 static inline void pq_update(struct hfi1_user_sdma_pkt_q *pq)
 {
-	if (atomic_dec_and_test(&pq->n_reqs)) {
-		xchg(&pq->state, SDMA_PKT_Q_INACTIVE);
+	if (atomic_dec_and_test(&pq->n_reqs))
 		wake_up(&pq->wait);
-	}
 }
 
 static void user_sdma_free_request(struct user_sdma_request *req, bool unpin)

drivers/infiniband/hw/hfi1/user_sdma.h

@@ -105,9 +105,10 @@ static inline int ahg_header_set(u32 *arr, int idx, size_t array_size,
 #define TXREQ_FLAGS_REQ_ACK   BIT(0)      /* Set the ACK bit in the header */
 #define TXREQ_FLAGS_REQ_DISABLE_SH BIT(1) /* Disable header suppression */
 
-#define SDMA_PKT_Q_INACTIVE BIT(0)
-#define SDMA_PKT_Q_ACTIVE   BIT(1)
-#define SDMA_PKT_Q_DEFERRED BIT(2)
+enum pkt_q_sdma_state {
+	SDMA_PKT_Q_ACTIVE,
+	SDMA_PKT_Q_DEFERRED,
+};
 
 /*
  * Maximum retry attempts to submit a TX request
@@ -133,7 +134,7 @@ struct hfi1_user_sdma_pkt_q {
 	struct user_sdma_request *reqs;
 	unsigned long *req_in_use;
 	struct iowait busy;
-	unsigned state;
+	enum pkt_q_sdma_state state;
 	wait_queue_head_t wait;
 	unsigned long unpinned;
 	struct mmu_rb_handler *handler;