net: mscc: ocelot: fix mutex lock error during ethtool stats read

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>
Link: https://lore.kernel.org/all/20220210150451.416845-2-colin.foster@in-advantage.com/
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/ethernet/mscc/ocelot.c b/drivers/net/ethernet/mscc/ocelot.c
index 354e4474bcc3b4717416899104bb313b0aff2ce4..e6de86552df0eeb433ca68a7de88210647720c17 100644 (file)
--- 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);