linux-kernel - [PATCH v3 18/18] ibmvfc: drop host lock when completing commands in CRQ

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Date:   Wed,  2 Dec 2020 20:08:06 -0600
From:   Tyrel Datwyler <tyreld@...ux.ibm.com>
To:     james.bottomley@...senpartnership.com
Cc:     martin.petersen@...cle.com, linux-scsi@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org,
        brking@...ux.ibm.com, Tyrel Datwyler <tyreld@...ux.ibm.com>
Subject: [PATCH v3 18/18] ibmvfc: drop host lock when completing commands in CRQ

The legacy CRQ holds the host lock the even while completing commands.
This presents a problem when in legacy single queue mode and
nr_hw_queues is greater than one since calling scsi_done() introduces
the potential for deadlock.

If nr_hw_queues is greater than one drop the hostlock in the legacy CRQ
path when completing a command.

Signed-off-by: Tyrel Datwyler <tyreld@...ux.ibm.com>
---
 drivers/scsi/ibmvscsi/ibmvfc.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/scsi/ibmvscsi/ibmvfc.c b/drivers/scsi/ibmvscsi/ibmvfc.c
index e499599662ec..e2200bdff2be 100644
--- a/drivers/scsi/ibmvscsi/ibmvfc.c
+++ b/drivers/scsi/ibmvscsi/ibmvfc.c
@@ -2969,6 +2969,7 @@ static void ibmvfc_handle_crq(struct ibmvfc_crq *crq, struct ibmvfc_host *vhost)
 {
 	long rc;
 	struct ibmvfc_event *evt = (struct ibmvfc_event *)be64_to_cpu(crq->ioba);
+	unsigned long flags;
 
 	switch (crq->valid) {
 	case IBMVFC_CRQ_INIT_RSP:
@@ -3039,7 +3040,12 @@ static void ibmvfc_handle_crq(struct ibmvfc_crq *crq, struct ibmvfc_host *vhost)
 	del_timer(&evt->timer);
 	list_del(&evt->queue);
 	ibmvfc_trc_end(evt);
-	evt->done(evt);
+	if (nr_scsi_hw_queues > 1) {
+		spin_unlock_irqrestore(vhost->host->host_lock, flags);
+		evt->done(evt);
+		spin_lock_irqsave(vhost->host->host_lock, flags);
+	} else
+		evt->done(evt);
 }
 
 /**
-- 
2.27.0