IB/hfi1: Avoid hardlockup with flushlist_lock

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>

diff --git a/drivers/infiniband/hw/hfi1/sdma.c b/drivers/infiniband/hw/hfi1/sdma.c
index b011072..70828de 100644 (file)
--- 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: