[PATCH 5.4 134/154] can: statistics: use atomic access in hot path

Greg Kroah-Hartman
2025-04-08T12:08:14Z

From: Oliver Hartkopp <socketcan@hartkopp.net>

[ Upstream commit 80b5f90158d1364cbd80ad82852a757fc0692bf2 ]

In can_send() and can_receive() CAN messages and CAN filter matches are
counted to be visible in the CAN procfs files.

KCSAN detected a data race within can_send() when two CAN frames have
been generated by a timer event writing to the same CAN netdevice at the
same time. Use atomic operations to access the statistics in the hot path
to fix the KCSAN complaint.

Reported-by: syzbot+78ce4489b812515d5e4d@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/67cd717d.050a0220.e1a89.0006.GAE@google.com
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Reviewed-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Link: https://patch.msgid.link/20250310143353.3242-1-socketcan@hartkopp.net
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/can/af_can.c | 12 ++++++------
net/can/af_can.h | 12 ++++++------
net/can/proc.c | 46 +++++++++++++++++++++++++++-------------------
3 files changed, 39 insertions(+), 31 deletions(-)

diff --git a/net/can/af_can.c b/net/can/af_can.c
index bc06016a4fe90..d2fd12da30c60 100644
--- a/net/can/af_can.c
+++ b/net/can/af_can.c
@@ -288,8 +288,8 @@ int can_send(struct sk_buff *skb, int loop)
netif_rx_ni(newskb);

/* update statistics */
- pkg_stats->tx_frames++;
- pkg_stats->tx_frames_delta++;
+ atomic_long_inc(&pkg_stats->tx_frames);
+ atomic_long_inc(&pkg_stats->tx_frames_delta);

return 0;

@@ -647,8 +647,8 @@ static void can_receive(struct sk_buff *skb, struct net_device *dev)
int matches;

/* update statistics */
- pkg_stats->rx_frames++;
- pkg_stats->rx_frames_delta++;
+ atomic_long_inc(&pkg_stats->rx_frames);
+ atomic_long_inc(&pkg_stats->rx_frames_delta);

/* create non-zero unique skb identifier together with *skb */
while (!(can_skb_prv(skb)->skbcnt))
@@ -669,8 +669,8 @@ static void can_receive(struct sk_buff *skb, struct net_device *dev)
consume_skb(skb);

if (matches > 0) {
- pkg_stats->matches++;
- pkg_stats->matches_delta++;
+ atomic_long_inc(&pkg_stats->matches);
+ atomic_long_inc(&pkg_stats->matches_delta);
}
}

diff --git a/net/can/af_can.h b/net/can/af_can.h
index 7c2d9161e2245..22f3352c77fec 100644
--- a/net/can/af_can.h
+++ b/net/can/af_can.h
@@ -66,9 +66,9 @@ struct receiver {
struct can_pkg_stats {
unsigned long jiffies_init;

- unsigned long rx_frames;
- unsigned long tx_frames;
- unsigned long matches;
+ atomic_long_t rx_frames;
+ atomic_long_t tx_frames;
+ atomic_long_t matches;

unsigned long total_rx_rate;
unsigned long total_tx_rate;
@@ -82,9 +82,9 @@ struct can_pkg_stats {
unsigned long max_tx_rate;
unsigned long max_rx_match_ratio;

- unsigned long rx_frames_delta;
- unsigned long tx_frames_delta;
- unsigned long matches_delta;
+ atomic_long_t rx_frames_delta;
+ atomic_long_t tx_frames_delta;
+ atomic_long_t matches_delta;
};

/* persistent statistics */
diff --git a/net/can/proc.c b/net/can/proc.c
index a5fc63c78370e..ea442ddd4fd9d 100644
--- a/net/can/proc.c
+++ b/net/can/proc.c
@@ -123,6 +123,13 @@ void can_stat_update(struct timer_list *t)
struct can_pkg_stats *pkg_stats = net->can.pkg_stats;
unsigned long j = jiffies; /* snapshot */

+ long rx_frames = atomic_long_read(&pkg_stats->rx_frames);
+ long tx_frames = atomic_long_read(&pkg_stats->tx_frames);
+ long matches = atomic_long_read(&pkg_stats->matches);
+ long rx_frames_delta = atomic_long_read(&pkg_stats->rx_frames_delta);
+ long tx_frames_delta = atomic_long_read(&pkg_stats->tx_frames_delta);
+ long matches_delta = atomic_long_read(&pkg_stats->matches_delta);
+
/* restart counting in timer context on user request */
if (user_reset)
can_init_stats(net);
@@ -132,35 +139,33 @@ void can_stat_update(struct timer_list *t)
can_init_stats(net);

/* prevent overflow in calc_rate() */
- if (pkg_stats->rx_frames > (ULONG_MAX / HZ))
+ if (rx_frames > (LONG_MAX / HZ))
can_init_stats(net);

/* prevent overflow in calc_rate() */
- if (pkg_stats->tx_frames > (ULONG_MAX / HZ))
+ if (tx_frames > (LONG_MAX / HZ))
can_init_stats(net);

/* matches overflow - very improbable */
- if (pkg_stats->matches > (ULONG_MAX / 100))
+ if (matches > (LONG_MAX / 100))
can_init_stats(net);

/* calc total values */
- if (pkg_stats->rx_frames)
- pkg_stats->total_rx_match_ratio = (pkg_stats->matches * 100) /
- pkg_stats->rx_frames;
+ if (rx_frames)
+ pkg_stats->total_rx_match_ratio = (matches * 100) / rx_frames;

pkg_stats->total_tx_rate = calc_rate(pkg_stats->jiffies_init, j,
- pkg_stats->tx_frames);
+ tx_frames);
pkg_stats->total_rx_rate = calc_rate(pkg_stats->jiffies_init, j,
- pkg_stats->rx_frames);
+ rx_frames);

/* calc current values */
- if (pkg_stats->rx_frames_delta)
+ if (rx_frames_delta)
pkg_stats->current_rx_match_ratio =
- (pkg_stats->matches_delta * 100) /
- pkg_stats->rx_frames_delta;
+ (matches_delta * 100) / rx_frames_delta;

- pkg_stats->current_tx_rate = calc_rate(0, HZ, pkg_stats->tx_frames_delta);
- pkg_stats->current_rx_rate = calc_rate(0, HZ, pkg_stats->rx_frames_delta);
+ pkg_stats->current_tx_rate = calc_rate(0, HZ, tx_frames_delta);
+ pkg_stats->current_rx_rate = calc_rate(0, HZ, rx_frames_delta);

/* check / update maximum values */
if (pkg_stats->max_tx_rate < pkg_stats->current_tx_rate)
@@ -173,9 +178,9 @@ void can_stat_update(struct timer_list *t)
pkg_stats->max_rx_match_ratio = pkg_stats->current_rx_match_ratio;

/* clear values for 'current rate' calculation */
- pkg_stats->tx_frames_delta = 0;
- pkg_stats->rx_frames_delta = 0;
- pkg_stats->matches_delta = 0;
+ atomic_long_set(&pkg_stats->tx_frames_delta, 0);
+ atomic_long_set(&pkg_stats->rx_frames_delta, 0);
+ atomic_long_set(&pkg_stats->matches_delta, 0);

/* restart timer (one second) */
mod_timer(&net->can.stattimer, round_jiffies(jiffies + HZ));
@@ -217,9 +222,12 @@ static int can_stats_proc_show(struct seq_file *m, void *v)
struct can_rcv_lists_stats *rcv_lists_stats = net->can.rcv_lists_stats;

seq_putc(m, '\n');
- seq_printf(m, " %8ld transmitted frames (TXF)\n", pkg_stats->tx_frames);
- seq_printf(m, " %8ld received frames (RXF)\n", pkg_stats->rx_frames);
- seq_printf(m, " %8ld matched frames (RXMF)\n", pkg_stats->matches);
+ seq_printf(m, " %8ld transmitted frames (TXF)\n",
+ atomic_long_read(&pkg_stats->tx_frames));
+ seq_printf(m, " %8ld received frames (RXF)\n",
+ atomic_long_read(&pkg_stats->rx_frames));
+ seq_printf(m, " %8ld matched frames (RXMF)\n",
+ atomic_long_read(&pkg_stats->matches));

seq_putc(m, '\n');

--
2.39.5