IB/hfi1: Avoid hardlockup with flushlist_lock

commit cf131a8 upstream.

Heavy contention of the sde flushlist_lock can cause hard lockups at
extreme scale when the flushing logic is under stress.

Mitigate by replacing the item at a time copy to the local list with
an O(1) list_splice_init() and using the high priority work queue to
do the flushes.

Ported to linux-4.9.y.

Fixes: 7724105 ("IB/hfi1: add driver files")
Cc: <[email protected]>
Reviewed-by: Dennis Dalessandro <[email protected]>
Signed-off-by: Mike Marciniszyn <[email protected]>
Signed-off-by: Dennis Dalessandro <[email protected]>
Signed-off-by: Doug Ledford <[email protected]>
Signed-off-by: Sasha Levin <[email protected]>

Author: Mike Marciniszyn

drivers/infiniband/hw/hfi1/sdma.c

@@ -410,10 +410,7 @@ static void sdma_flush(struct sdma_engine *sde)
 	sdma_flush_descq(sde);
 	spin_lock_irqsave(&sde->flushlist_lock, flags);
 	/* copy flush list */
-	list_for_each_entry_safe(txp, txp_next, &sde->flushlist, list) {
-		list_del_init(&txp->list);
-		list_add_tail(&txp->list, &flushlist);
-	}
+	list_splice_init(&sde->flushlist, &flushlist);
 	spin_unlock_irqrestore(&sde->flushlist_lock, flags);
 	/* flush from flush list */
 	list_for_each_entry_safe(txp, txp_next, &flushlist, list)
@@ -2406,7 +2403,7 @@ int sdma_send_txreq(struct sdma_engine *sde,
 		wait->tx_count++;
 		wait->count += tx->num_desc;
 	}
-	schedule_work(&sde->flush_worker);
+	queue_work_on(sde->cpu, system_highpri_wq, &sde->flush_worker);
 	ret = -ECOMM;
 	goto unlock;
 nodesc:
@@ -2504,7 +2501,7 @@ int sdma_send_txlist(struct sdma_engine *sde, struct iowait *wait,
 		}
 	}
 	spin_unlock(&sde->flushlist_lock);
-	schedule_work(&sde->flush_worker);
+	queue_work_on(sde->cpu, system_highpri_wq, &sde->flush_worker);
 	ret = -ECOMM;
 	goto update_tail;
 nodesc: