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FAILED: patch "[PATCH] can: bcm: use call_rcu() instead of costly synchronize_rcu()" failed to apply to 4.14-stable tree

PATCH [email protected] 1 participant 1 message Jul 8, 2022

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The patch below does not apply to the 4.14-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From f1b4e32aca0811aa011c76e5d6cf2fa19224b386 Mon Sep 17 00:00:00 2001
From: Oliver Hartkopp <[email protected]>
Date: Fri, 20 May 2022 20:32:39 +0200
Subject: [PATCH] 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/[email protected] open here
Cc [email protected]
Cc Eric Dumazet <[email protected]>
Cc Norbert Slusarek <[email protected]>
Cc Thadeu Lima de Souza Cascardo <[email protected]>
Signed-off-by Oliver Hartkopp <[email protected]>
Signed-off-by Marc Kleine-Budde <[email protected]>
net/can/bcm.c +14 -4
index 65ee1b784a30..e60161bec850 100644
@@ -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 */
 		}