[PATCH net v4 6/6] can: rockchip_canfd: serialize timecounter timestamp conversion

[Cunhao Lu via B4 Relay]

From: Cunhao Lu <1579567540 at qq.com>

The timestamp worker advances the timecounter with timecounter_read()
while RX, TX completion and error-frame paths use timecounter_cyc2time()
to convert hardware timestamps without holding timestamp_lock.

timecounter_read() updates frac, cycle_last and nsec in separate steps.
A concurrent conversion can observe the new cycle_last with the old
nsec and produce an incorrect timestamp.

Hold timestamp_lock across timecounter_cyc2time(), using the same lock
as timecounter_read() and timecounter_init(). Keep the SKB timestamp
assignment outside the critical section.

TX completion nests timestamp_lock inside tx_lock; no timestamp-lock
holder acquires tx_lock.

Fixes: 4e1a18bab124 ("can: rockchip_canfd: add hardware timestamping support")
Cc: stable at vger.kernel.org
Signed-off-by: Cunhao Lu <1579567540 at qq.com>
---
 drivers/net/can/rockchip/rockchip_canfd-timestamp.c | 5 ++++-
 drivers/net/can/rockchip/rockchip_canfd.h           | 4 ++--
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/net/can/rockchip/rockchip_canfd-timestamp.c b/drivers/net/can/rockchip/rockchip_canfd-timestamp.c
index 0fa791849c95..05f1005ee506 100644
--- a/drivers/net/can/rockchip/rockchip_canfd-timestamp.c
+++ b/drivers/net/can/rockchip/rockchip_canfd-timestamp.c
@@ -15,13 +15,16 @@ static u64 rkcanfd_timestamp_read(struct cyclecounter *cc)
 	return rkcanfd_get_timestamp(priv);
 }
 
-void rkcanfd_skb_set_timestamp(const struct rkcanfd_priv *priv,
+void rkcanfd_skb_set_timestamp(struct rkcanfd_priv *priv,
 			       struct sk_buff *skb, const u32 timestamp)
 {
 	struct skb_shared_hwtstamps *hwtstamps = skb_hwtstamps(skb);
+	unsigned long flags;
 	u64 ns;
 
+	spin_lock_irqsave(&priv->timestamp_lock, flags);
 	ns = timecounter_cyc2time(&priv->tc, timestamp);
+	spin_unlock_irqrestore(&priv->timestamp_lock, flags);
 
 	hwtstamps->hwtstamp = ns_to_ktime(ns);
 }
diff --git a/drivers/net/can/rockchip/rockchip_canfd.h b/drivers/net/can/rockchip/rockchip_canfd.h
index 4a2bdc205296..63f146ff8e6b 100644
--- a/drivers/net/can/rockchip/rockchip_canfd.h
+++ b/drivers/net/can/rockchip/rockchip_canfd.h
@@ -489,7 +489,7 @@ struct rkcanfd_priv {
 
 	struct cyclecounter cc;
 	struct timecounter tc;
-	/* Protects timestamp_active and worker reads/requeueing. */
+	/* Protects tc, timestamp_active and worker requeueing. */
 	spinlock_t timestamp_lock;
 	struct delayed_work timestamp;
 	unsigned long work_delay_jiffies;
@@ -557,7 +557,7 @@ void rkcanfd_ethtool_init(struct rkcanfd_priv *priv);
 
 int rkcanfd_handle_rx_int(struct rkcanfd_priv *priv);
 
-void rkcanfd_skb_set_timestamp(const struct rkcanfd_priv *priv,
+void rkcanfd_skb_set_timestamp(struct rkcanfd_priv *priv,
 			       struct sk_buff *skb, const u32 timestamp);
 void rkcanfd_timestamp_work_init(struct rkcanfd_priv *priv);
 void rkcanfd_timestamp_init(struct rkcanfd_priv *priv);

-- 
2.34.1