linux-kernel - [PATCH AUTOSEL 4.14 001/109] s390/qeth: invoke softirqs after napi

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Date:   Sat,  9 Nov 2019 21:43:53 -0500
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Julian Wiedmann <jwi@...ux.ibm.com>,
        "David S . Miller" <davem@...emloft.net>,
        Sasha Levin <sashal@...nel.org>, linux-s390@...r.kernel.org
Subject: [PATCH AUTOSEL 4.14 001/109] s390/qeth: invoke softirqs after napi_schedule()

From: Julian Wiedmann <jwi@...ux.ibm.com>

[ Upstream commit 4d19db777a2f32c9b76f6fd517ed8960576cb43e ]

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>
Signed-off-by: David S. Miller <davem@...emloft.net>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 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 2845316db5545..6fa07c2469150 100644
--- a/drivers/s390/net/qeth_l2_main.c
+++ b/drivers/s390/net/qeth_l2_main.c
@@ -869,7 +869,10 @@ 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 d9830c86d0c11..8bccfd686b735 100644
--- a/drivers/s390/net/qeth_l3_main.c
+++ b/drivers/s390/net/qeth_l3_main.c
@@ -2849,7 +2849,10 @@ 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;
-- 
2.20.1