linux-kernel - [PATCH 3.16 031/305] s390/qeth: invoke softirqs after napi

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Date:   Sun, 03 Feb 2019 14:45:08 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Julian Wiedmann" <jwi@...ux.ibm.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: [PATCH 3.16 031/305] s390/qeth: invoke softirqs after napi_schedule()

3.16.63-rc1 review patch.  If anyone has any objections, please let me know.

------------------

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

commit 4d19db777a2f32c9b76f6fd517ed8960576cb43e upstream.

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: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/s390/net/qeth_l2_main.c | 3 +++
 drivers/s390/net/qeth_l3_main.c | 3 +++
 2 files changed, 6 insertions(+)

--- a/drivers/s390/net/qeth_l2_main.c
+++ b/drivers/s390/net/qeth_l2_main.c
@@ -856,7 +856,10 @@ static int __qeth_l2_open(struct net_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;
--- a/drivers/s390/net/qeth_l3_main.c
+++ b/drivers/s390/net/qeth_l3_main.c
@@ -3127,7 +3127,10 @@ static int __qeth_l3_open(struct net_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;