linux-kernel - [PATCH net 3/3] net: dsa: felix: access QSYS_TAG_CONFIG under tas_lock in vsc9959_sched_speed

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Date:   Sat,  3 Sep 2022 00:57:02 +0300
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     netdev@...r.kernel.org
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Xiaoliang Yang <xiaoliang.yang_1@....com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        UNGLinuxDriver@...rochip.com, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Michael Walle <michael@...le.cc>,
        Vinicius Costa Gomes <vinicius.gomes@...el.com>,
        Maxim Kochetkov <fido_max@...ox.ru>,
        Colin Foster <colin.foster@...advantage.com>,
        Richie Pearn <richard.pearn@....com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH net 3/3] net: dsa: felix: access QSYS_TAG_CONFIG under tas_lock in vsc9959_sched_speed_set

The read-modify-write of QSYS_TAG_CONFIG from vsc9959_sched_speed_set()
runs unlocked with respect to the other functions that access it, which
are vsc9959_tas_guard_bands_update(), vsc9959_qos_port_tas_set() and
vsc9959_tas_clock_adjust(). All the others are under ocelot->tas_lock,
so move the vsc9959_sched_speed_set() access under that lock as well, to
resolve the concurrency.

Fixes: 55a515b1f5a9 ("net: dsa: felix: drop oversized frames with tc-taprio instead of hanging the port")
Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
---
 drivers/net/dsa/ocelot/felix_vsc9959.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/net/dsa/ocelot/felix_vsc9959.c b/drivers/net/dsa/ocelot/felix_vsc9959.c
index 35ce08b485f3..db0aec807965 100644
--- a/drivers/net/dsa/ocelot/felix_vsc9959.c
+++ b/drivers/net/dsa/ocelot/felix_vsc9959.c
@@ -1741,13 +1741,13 @@ static void vsc9959_sched_speed_set(struct ocelot *ocelot, int port,
 		break;
 	}
 
+	mutex_lock(&ocelot->tas_lock);
+
 	ocelot_rmw_rix(ocelot,
 		       QSYS_TAG_CONFIG_LINK_SPEED(tas_speed),
 		       QSYS_TAG_CONFIG_LINK_SPEED_M,
 		       QSYS_TAG_CONFIG, port);
 
-	mutex_lock(&ocelot->tas_lock);
-
 	if (ocelot_port->taprio)
 		vsc9959_tas_guard_bands_update(ocelot, port);
 
-- 
2.34.1