[PATCH net v2] net: dsa: mt7530: fix .get_stats64 sleeping in atomic context

Daniel Golle
2026-04-19T10:43:35Z

The .get_stats64 callback runs in atomic context, but on
MDIO-connected switches every register read acquires the MDIO bus
mutex, which can sleep:
[ 12.645973] BUG: sleeping function called from invalid context at kernel/locking/mutex.c:609
[ 12.654442] in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 759, name: grep
[ 12.663377] preempt_count: 0, expected: 0
[ 12.667410] RCU nest depth: 1, expected: 0
[ 12.671511] INFO: lockdep is turned off.
[ 12.675441] CPU: 0 UID: 0 PID: 759 Comm: grep Tainted: G S W 7.0.0+ #0 PREEMPT
[ 12.675453] Tainted: [S]=CPU_OUT_OF_SPEC, [W]=WARN
[ 12.675456] Hardware name: Bananapi BPI-R64 (DT)
[ 12.675459] Call trace:
[ 12.675462] show_stack+0x14/0x1c (C)
[ 12.675477] dump_stack_lvl+0x68/0x8c
[ 12.675487] dump_stack+0x14/0x1c
[ 12.675495] __might_resched+0x14c/0x220
[ 12.675504] __might_sleep+0x44/0x80
[ 12.675511] __mutex_lock+0x50/0xb10
[ 12.675523] mutex_lock_nested+0x20/0x30
[ 12.675532] mt7530_get_stats64+0x40/0x2ac
[ 12.675542] dsa_user_get_stats64+0x2c/0x40
[ 12.675553] dev_get_stats+0x44/0x1e0
[ 12.675564] dev_seq_printf_stats+0x24/0xe0
[ 12.675575] dev_seq_show+0x14/0x3c
[ 12.675583] seq_read_iter+0x37c/0x480
[ 12.675595] seq_read+0xd0/0xec
[ 12.675605] proc_reg_read+0x94/0xe4
[ 12.675615] vfs_read+0x98/0x29c
[ 12.675625] ksys_read+0x54/0xdc
[ 12.675633] __arm64_sys_read+0x18/0x20
[ 12.675642] invoke_syscall.constprop.0+0x54/0xec
[ 12.675653] do_el0_svc+0x3c/0xb4
[ 12.675662] el0_svc+0x38/0x200
[ 12.675670] el0t_64_sync_handler+0x98/0xdc
[ 12.675679] el0t_64_sync+0x158/0x15c

For MDIO-connected switches, poll MIB counters asynchronously using a
delayed workqueue every second and let .get_stats64 return the cached
values under a spinlock. A mod_delayed_work() call on each read
triggers an immediate refresh so counters stay responsive when queried
more frequently.

MMIO-connected switches (MT7988, EN7581, AN7583) are not affected
because their regmap does not sleep, so they continue to read MIB
counters directly in .get_stats64.

Fixes: 88c810f35ed5 ("net: dsa: mt7530: implement .get_stats64")
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Acked-by: Chester A. Unal <chester.a.unal@arinc9.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
---
v2:
* use spin_lock_bh()/spin_unlock_bh() to prevent potential deadlock
* rate-limit mod_delayed_work() refresh to at most once per 100ms
* move cancel_delayed_work_sync() after dsa_unregister_switch()
* add mt753x_teardown() callback to cancel the stats work
* fix commit message

drivers/net/dsa/mt7530.c | 66 ++++++++++++++++++++++++++++++++++++++--
drivers/net/dsa/mt7530.h | 8 +++++
2 files changed, 71 insertions(+), 3 deletions(-)

diff --git a/drivers/net/dsa/mt7530.c b/drivers/net/dsa/mt7530.c
index b9423389c2ef0..8c1186ba2279b 100644
--- a/drivers/net/dsa/mt7530.c
+++ b/drivers/net/dsa/mt7530.c
@@ -25,6 +25,9 @@

#include "mt7530.h"

+#define MT7530_STATS_POLL_INTERVAL (1 * HZ)
+#define MT7530_STATS_RATE_LIMIT (HZ / 10)
+
static struct mt753x_pcs *pcs_to_mt753x_pcs(struct phylink_pcs *pcs)
{
return container_of(pcs, struct mt753x_pcs, pcs);
@@ -906,10 +909,9 @@ static void mt7530_get_rmon_stats(struct dsa_switch *ds, int port,
*ranges = mt7530_rmon_ranges;
}

-static void mt7530_get_stats64(struct dsa_switch *ds, int port,
- struct rtnl_link_stats64 *storage)
+static void mt7530_read_port_stats64(struct mt7530_priv *priv, int port,
+ struct rtnl_link_stats64 *storage)
{
- struct mt7530_priv *priv = ds->priv;
uint64_t data;

/* MIB counter doesn't provide a FramesTransmittedOK but instead
@@ -951,6 +953,45 @@ static void mt7530_get_stats64(struct dsa_switch *ds, int port,
&storage->rx_crc_errors);
}

+static void mt7530_stats_poll(struct work_struct *work)
+{
+ struct mt7530_priv *priv = container_of(work, struct mt7530_priv,
+ stats_work.work);
+ struct rtnl_link_stats64 stats = {};
+ struct dsa_port *dp;
+ int port;
+
+ dsa_switch_for_each_user_port(dp, priv->ds) {
+ port = dp->index;
+
+ mt7530_read_port_stats64(priv, port, &stats);
+
+ spin_lock_bh(&priv->stats_lock);
+ priv->ports[port].stats = stats;
+ spin_unlock_bh(&priv->stats_lock);
+ }
+
+ priv->stats_last = jiffies;
+ schedule_delayed_work(&priv->stats_work,
+ MT7530_STATS_POLL_INTERVAL);
+}
+
+static void mt7530_get_stats64(struct dsa_switch *ds, int port,
+ struct rtnl_link_stats64 *storage)
+{
+ struct mt7530_priv *priv = ds->priv;
+
+ if (priv->bus) {
+ spin_lock_bh(&priv->stats_lock);
+ *storage = priv->ports[port].stats;
+ spin_unlock_bh(&priv->stats_lock);
+ if (time_after(jiffies, priv->stats_last + MT7530_STATS_RATE_LIMIT))
+ mod_delayed_work(system_wq, &priv->stats_work, 0);
+ } else {
+ mt7530_read_port_stats64(priv, port, storage);
+ }
+}
+
static void mt7530_get_eth_ctrl_stats(struct dsa_switch *ds, int port,
struct ethtool_eth_ctrl_stats *ctrl_stats)
{
@@ -3137,9 +3178,24 @@ mt753x_setup(struct dsa_switch *ds)
if (ret && priv->irq_domain)
mt7530_free_mdio_irq(priv);

+ if (!ret && priv->bus) {
+ spin_lock_init(&priv->stats_lock);
+ INIT_DELAYED_WORK(&priv->stats_work, mt7530_stats_poll);
+ schedule_delayed_work(&priv->stats_work,
+ MT7530_STATS_POLL_INTERVAL);
+ }
+
return ret;
}

+static void mt753x_teardown(struct dsa_switch *ds)
+{
+ struct mt7530_priv *priv = ds->priv;
+
+ if (priv->bus)
+ cancel_delayed_work_sync(&priv->stats_work);
+}
+
static int mt753x_set_mac_eee(struct dsa_switch *ds, int port,
struct ethtool_keee *e)
{
@@ -3257,6 +3313,7 @@ static int mt7988_setup(struct dsa_switch *ds)
static const struct dsa_switch_ops mt7530_switch_ops = {
.get_tag_protocol = mtk_get_tag_protocol,
.setup = mt753x_setup,
+ .teardown = mt753x_teardown,
.preferred_default_local_cpu_port = mt753x_preferred_default_local_cpu_port,
.get_strings = mt7530_get_strings,
.get_ethtool_stats = mt7530_get_ethtool_stats,
@@ -3409,6 +3466,9 @@ mt7530_remove_common(struct mt7530_priv *priv)

dsa_unregister_switch(priv->ds);

+ if (priv->bus)
+ cancel_delayed_work_sync(&priv->stats_work);
+
mutex_destroy(&priv->reg_mutex);
}
EXPORT_SYMBOL_GPL(mt7530_remove_common);
diff --git a/drivers/net/dsa/mt7530.h b/drivers/net/dsa/mt7530.h
index 3e0090bed298d..dd33b0df3419e 100644
--- a/drivers/net/dsa/mt7530.h
+++ b/drivers/net/dsa/mt7530.h
@@ -796,6 +796,7 @@ struct mt7530_fdb {
* @pvid: The VLAN specified is to be considered a PVID at ingress. Any
* untagged frames will be assigned to the related VLAN.
* @sgmii_pcs: Pointer to PCS instance for SerDes ports
+ * @stats: Cached port statistics for MDIO-connected switches
*/
struct mt7530_port {
bool enable;
@@ -803,6 +804,7 @@ struct mt7530_port {
u32 pm;
u16 pvid;
struct phylink_pcs *sgmii_pcs;
+ struct rtnl_link_stats64 stats;
};

/* Port 5 mode definitions of the MT7530 switch */
@@ -875,6 +877,9 @@ struct mt753x_info {
* @create_sgmii: Pointer to function creating SGMII PCS instance(s)
* @active_cpu_ports: Holding the active CPU ports
* @mdiodev: The pointer to the MDIO device structure
+ * @stats_lock: Protects cached per-port stats from concurrent access
+ * @stats_work: Delayed work for polling MIB counters on MDIO switches
+ * @stats_last: Jiffies timestamp of last MIB counter poll
*/
struct mt7530_priv {
struct device *dev;
@@ -900,6 +905,9 @@ struct mt7530_priv {
int (*create_sgmii)(struct mt7530_priv *priv);
u8 active_cpu_ports;
struct mdio_device *mdiodev;
+ spinlock_t stats_lock; /* protects cached stats counters */
+ struct delayed_work stats_work;
+ unsigned long stats_last;
};

struct mt7530_hw_vlan_entry {
--
2.53.0