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From:   Colin Foster <colin.foster@in-advantage.com>
To:     linux-kernel@vger.kernel.org, netdev@vger.kernel.org
Cc:     Andrew Lunn <andrew@lunn.ch>, Jakub Kicinski <kuba@kernel.org>,
        "David S. Miller" <davem@davemloft.net>,
        UNGLinuxDriver@microchip.com,
        Alexandre Belloni <alexandre.belloni@bootlin.com>,
        Claudiu Manoil <claudiu.manoil@nxp.com>,
        Vladimir Oltean <vladimir.oltean@nxp.com>
Subject: [PATCH v1 net 1/1] net: mscc: ocelot: fix mutex lock error during ethtool stats read
Date:   Thu, 10 Feb 2022 07:04:51 -0800
Message-Id: <20220210150451.416845-2-colin.foster@in-advantage.com>
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An ongoing workqueue populates the stats buffer. At the same time, a user
might query the statistics. While writing to the buffer is mutex-locked,
reading from the buffer wasn't. This could lead to buggy reads by ethtool.

This patch fixes the former blamed commit, but the bug was introduced in
the latter.

Signed-off-by: Colin Foster <colin.foster@in-advantage.com>
Fixes: 1e1caa9735f90 ("ocelot: Clean up stats update deferred work")
Fixes: a556c76adc052 ("net: mscc: Add initial Ocelot switch support")
Reported-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
---
 drivers/net/ethernet/mscc/ocelot.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/mscc/ocelot.c b/drivers/net/ethernet/mscc/ocelot.c
index 354e4474bcc3..e6de86552df0 100644
--- a/drivers/net/ethernet/mscc/ocelot.c
+++ b/drivers/net/ethernet/mscc/ocelot.c
@@ -1745,12 +1745,11 @@ void ocelot_get_strings(struct ocelot *ocelot, int port, u32 sset, u8 *data)
 }
 EXPORT_SYMBOL(ocelot_get_strings);
 
+/* Caller must hold &ocelot->stats_lock */
 static void ocelot_update_stats(struct ocelot *ocelot)
 {
 	int i, j;
 
-	mutex_lock(&ocelot->stats_lock);
-
 	for (i = 0; i < ocelot->num_phys_ports; i++) {
 		/* Configure the port to read the stats from */
 		ocelot_write(ocelot, SYS_STAT_CFG_STAT_VIEW(i), SYS_STAT_CFG);
@@ -1769,8 +1768,6 @@ static void ocelot_update_stats(struct ocelot *ocelot)
 					      ~(u64)U32_MAX) + val;
 		}
 	}
-
-	mutex_unlock(&ocelot->stats_lock);
 }
 
 static void ocelot_check_stats_work(struct work_struct *work)
@@ -1779,7 +1776,9 @@ static void ocelot_check_stats_work(struct work_struct *work)
 	struct ocelot *ocelot = container_of(del_work, struct ocelot,
 					     stats_work);
 
+	mutex_lock(&ocelot->stats_lock);
 	ocelot_update_stats(ocelot);
+	mutex_unlock(&ocelot->stats_lock);
 
 	queue_delayed_work(ocelot->stats_queue, &ocelot->stats_work,
 			   OCELOT_STATS_CHECK_DELAY);
@@ -1789,12 +1788,16 @@ void ocelot_get_ethtool_stats(struct ocelot *ocelot, int port, u64 *data)
 {
 	int i;
 
+	mutex_lock(&ocelot->stats_lock);
+
 	/* check and update now */
 	ocelot_update_stats(ocelot);
 
 	/* Copy all counters */
 	for (i = 0; i < ocelot->num_stats; i++)
 		*data++ = ocelot->stats[port * ocelot->num_stats + i];
+
+	mutex_unlock(&ocelot->stats_lock);
 }
 EXPORT_SYMBOL(ocelot_get_ethtool_stats);
 
-- 
2.25.1