IB/hfi1: Fix abba locking issue with sc_disable()

sc_disable() after having disabled the send context wakes up any waiters
by calling hfi1_qp_wakeup() while holding the waitlock for the sc.

This is contrary to the model for all other calls to hfi1_qp_wakeup()
where the waitlock is dropped and a local is used to drive calls to
hfi1_qp_wakeup().

Fix by moving the sc->piowait into a local list and driving the wakeup
calls from the list.

Fixes: 099a884 ("IB/hfi1: Handle wakeup of orphaned QPs for pio")
Link: https://lore.kernel.org/r/20211013141852.128104.2682.stgit@awfm-01.cornelisnetworks.com
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@cornelisnetworks.com>
Reported-by: TOTE Robot <oslab@tsinghua.edu.cn>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/hw/hfi1/pio.c

@@ -878,6 +878,7 @@ void sc_disable(struct send_context *sc)
 {
 	u64 reg;
 	struct pio_buf *pbuf;
+	LIST_HEAD(wake_list);
 
 	if (!sc)
 		return;
@@ -912,19 +913,21 @@ void sc_disable(struct send_context *sc)
 	spin_unlock(&sc->release_lock);
 
 	write_seqlock(&sc->waitlock);
-	while (!list_empty(&sc->piowait)) {
+	if (!list_empty(&sc->piowait))
+		list_move(&sc->piowait, &wake_list);
+	write_sequnlock(&sc->waitlock);
+	while (!list_empty(&wake_list)) {
 		struct iowait *wait;
 		struct rvt_qp *qp;
 		struct hfi1_qp_priv *priv;
 
-		wait = list_first_entry(&sc->piowait, struct iowait, list);
+		wait = list_first_entry(&wake_list, struct iowait, list);
 		qp = iowait_to_qp(wait);
 		priv = qp->priv;
 		list_del_init(&priv->s_iowait.list);
 		priv->s_iowait.lock = NULL;
 		hfi1_qp_wakeup(qp, RVT_S_WAIT_PIO | HFI1_S_WAIT_PIO_DRAIN);
 	}
-	write_sequnlock(&sc->waitlock);
 
 	spin_unlock_irq(&sc->alloc_lock);
 }