From cf131a81967583ae737df6383a0893b9fee75b4e Mon Sep 17 00:00:00 2001
From: Mike Marciniszyn <mike.marciniszyn@intel.com>
Date: Fri, 14 Jun 2019 12:32:26 -0400
Subject: [PATCH 1/1] IB/hfi1: Avoid hardlockup with flushlist_lock
Git-commit: cf131a81967583ae737df6383a0893b9fee75b4e
Patch-mainline: v5.10-rc1
References: bsc#1111666

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.

Fixes: 7724105686e7 ("IB/hfi1: add driver files")
Cc: <stable@vger.kernel.org>
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>
Acked-by: Nicolas Morey-Chaisemartin <nmoreychaisemartin@suse.com>
---
 drivers/infiniband/hw/hfi1/sdma.c | 9 +++------
 1 file changed, 3 insertions(+), 6 deletions(-)

diff --git a/drivers/infiniband/hw/hfi1/sdma.c b/drivers/infiniband/hw/hfi1/sdma.c
index b0110728f541..70828de7436b 100644
--- a/drivers/infiniband/hw/hfi1/sdma.c
+++ b/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)
@@ -2413,7 +2410,7 @@ unlock_noconn:
 	list_add_tail(&tx->list, &sde->flushlist);
 	spin_unlock(&sde->flushlist_lock);
 	iowait_inc_wait_count(wait, tx->num_desc);
-	schedule_work(&sde->flush_worker);
+	queue_work_on(sde->cpu, system_highpri_wq, &sde->flush_worker);
 	ret = -ECOMM;
 	goto unlock;
 nodesc:
@@ -2511,7 +2508,7 @@ unlock_noconn:
 		iowait_inc_wait_count(wait, tx->num_desc);
 	}
 	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:
-- 
2.26.2