[PATCH 5.15 007/230] can: bcm: use call_rcu() instead of costly synchronize_rcu()

Greg Kroah-Hartman
2022-07-11T09:43:12Z

From: Oliver Hartkopp <socketcan@hartkopp.net>

commit f1b4e32aca0811aa011c76e5d6cf2fa19224b386 upstream.

In commit d5f9023fa61e ("can: bcm: delay release of struct bcm_op
after synchronize_rcu()") Thadeu Lima de Souza Cascardo introduced two
synchronize_rcu() calls in bcm_release() (only once at socket close)
and in bcm_delete_rx_op() (called on removal of each single bcm_op).

Unfortunately this slow removal of the bcm_op's affects user space
applications like cansniffer where the modification of a filter
removes 2048 bcm_op's which blocks the cansniffer application for
40(!) seconds.

In commit 181d4447905d ("can: gw: use call_rcu() instead of costly
synchronize_rcu()") Eric Dumazet replaced the synchronize_rcu() calls
with several call_rcu()'s to safely remove the data structures after
the removal of CAN ID subscriptions with can_rx_unregister() calls.

This patch adopts Erics approach for the can-bcm which should be
applicable since the removal of tasklet_kill() in bcm_remove_op() and
the introduction of the HRTIMER_MODE_SOFT timer handling in Linux 5.4.

Fixes: d5f9023fa61e ("can: bcm: delay release of struct bcm_op after synchronize_rcu()") # >= 5.4
Link: https://lore.kernel.org/all/20220520183239.19111-1-socketcan@hartkopp.net
Cc: stable@vger.kernel.org
Cc: Eric Dumazet <edumazet@google.com>
Cc: Norbert Slusarek <nslusarek@gmx.net>
Cc: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/can/bcm.c | 18 ++++++++++++++----
1 file changed, 14 insertions(+), 4 deletions(-)

--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -100,6 +100,7 @@ static inline u64 get_u64(const struct c

struct bcm_op {
struct list_head list;
+ struct rcu_head rcu;
int ifindex;
canid_t can_id;
u32 flags;
@@ -718,10 +719,9 @@ static struct bcm_op *bcm_find_op(struct
return NULL;
}

-static void bcm_remove_op(struct bcm_op *op)
+static void bcm_free_op_rcu(struct rcu_head *rcu_head)
{
- hrtimer_cancel(&op->timer);
- hrtimer_cancel(&op->thrtimer);
+ struct bcm_op *op = container_of(rcu_head, struct bcm_op, rcu);

if ((op->frames) && (op->frames != &op->sframe))
kfree(op->frames);
@@ -732,6 +732,14 @@ static void bcm_remove_op(struct bcm_op
kfree(op);
}

+static void bcm_remove_op(struct bcm_op *op)
+{
+ hrtimer_cancel(&op->timer);
+ hrtimer_cancel(&op->thrtimer);
+
+ call_rcu(&op->rcu, bcm_free_op_rcu);
+}
+
static void bcm_rx_unreg(struct net_device *dev, struct bcm_op *op)
{
if (op->rx_reg_dev == dev) {
@@ -757,6 +765,9 @@ static int bcm_delete_rx_op(struct list_
if ((op->can_id == mh->can_id) && (op->ifindex == ifindex) &&
(op->flags & CAN_FD_FRAME) == (mh->flags & CAN_FD_FRAME)) {

+ /* disable automatic timer on frame reception */
+ op->flags |= RX_NO_AUTOTIMER;
+
/*
* Don't care if we're bound or not (due to netdev
* problems) can_rx_unregister() is always a save
@@ -785,7 +796,6 @@ static int bcm_delete_rx_op(struct list_
bcm_rx_handler, op);

list_del(&op->list);
- synchronize_rcu();
bcm_remove_op(op);
return 1; /* done */
}