netdev - [PATCH net-next 12/15] s390/qeth: invoke softirqs after napi

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Message-Id: <20180917153609.94628-13-jwi@linux.ibm.com>
Date:   Mon, 17 Sep 2018 17:36:06 +0200
From:   Julian Wiedmann <jwi@...ux.ibm.com>
To:     David Miller <davem@...emloft.net>
Cc:     <netdev@...r.kernel.org>, <linux-s390@...r.kernel.org>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Stefan Raspl <raspl@...ux.ibm.com>,
        Ursula Braun <ubraun@...ux.ibm.com>,
        Julian Wiedmann <jwi@...ux.ibm.com>
Subject: [PATCH net-next 12/15] s390/qeth: invoke softirqs after napi_schedule()

Calling napi_schedule() from process context does not ensure that the
NET_RX softirq is run in a timely fashion. So trigger it manually.

This is no big issue with current code. A call to ndo_open() is usually
followed by a ndo_set_rx_mode() call, and for qeth this contains a
spin_unlock_bh(). Except for OSN, where qeth_l2_set_rx_mode() bails out
early.
Nevertheless it's best to not depend on this behaviour, and just fix
the issue at its source like all other drivers do. For instance see
commit 83a0c6e58901 ("i40e: Invoke softirqs after napi_reschedule").

Fixes: a1c3ed4c9ca0 ("qeth: NAPI support for l2 and l3 discipline")
Signed-off-by: Julian Wiedmann <jwi@...ux.ibm.com>
---
 drivers/s390/net/qeth_l2_main.c | 3 +++
 drivers/s390/net/qeth_l3_main.c | 3 +++
 2 files changed, 6 insertions(+)

diff --git a/drivers/s390/net/qeth_l2_main.c b/drivers/s390/net/qeth_l2_main.c
index 33b65471a68a..6285af373bdf 100644
--- a/drivers/s390/net/qeth_l2_main.c
+++ b/drivers/s390/net/qeth_l2_main.c
@@ -755,7 +755,10 @@ static int __qeth_l2_open(struct net_device *dev)
 
 	if (qdio_stop_irq(card->data.ccwdev, 0) >= 0) {
 		napi_enable(&card->napi);
+		local_bh_disable();
 		napi_schedule(&card->napi);
+		/* kick-start the NAPI softirq: */
+		local_bh_enable();
 	} else
 		rc = -EIO;
 	return rc;
diff --git a/drivers/s390/net/qeth_l3_main.c b/drivers/s390/net/qeth_l3_main.c
index 5d7e2921ab36..8930d2a9fcad 100644
--- a/drivers/s390/net/qeth_l3_main.c
+++ b/drivers/s390/net/qeth_l3_main.c
@@ -2293,7 +2293,10 @@ static int __qeth_l3_open(struct net_device *dev)
 
 	if (qdio_stop_irq(card->data.ccwdev, 0) >= 0) {
 		napi_enable(&card->napi);
+		local_bh_disable();
 		napi_schedule(&card->napi);
+		/* kick-start the NAPI softirq: */
+		local_bh_enable();
 	} else
 		rc = -EIO;
 	return rc;
-- 
2.16.4