can: bcm: use call_rcu() instead of costly synchronize_rcu()

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>

diff --git a/net/can/bcm.c b/net/can/bcm.c
index 65ee1b7..e60161b 100644 (file)
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -100,6 +100,7 @@ static inline u64 get_u64(const struct canfd_frame *cp, int offset)
 
 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 list_head *ops,
        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 *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_head *ops, struct bcm_msg_head *mh,
                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_head *ops, struct bcm_msg_head *mh,
                                                  bcm_rx_handler, op);
 
                        list_del(&op->list);
-                       synchronize_rcu();
                        bcm_remove_op(op);
                        return 1; /* done */
                }