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Date: Tue, 2 Jan 2024 12:11:05 +0100
From: Jiri Pirko <jiri@...nulli.us>
To: David Wei <dw@...idwei.uk>
Cc: Jakub Kicinski <kuba@...nel.org>, Sabrina Dubroca <sd@...asysnail.net>,
netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCH net-next v5 2/5] netdevsim: allow two netdevsim ports to
be connected
Thu, Dec 28, 2023 at 02:46:30AM CET, dw@...idwei.uk wrote:
>Add a debugfs file in
>/sys/kernel/debug/netdevsim/netdevsimN/ports/A/peer
>
>Writing "M B" to this file will link port A of netdevsim N with port B
>of netdevsim M. Reading this file will return the linked netdevsim id
>and port, if any.
>
>During nsim_dev_peer_write(), nsim_dev_list_lock prevents concurrent
>modifications to nsim_dev and peer's devlink->lock prevents concurrent
>modifications to the peer's port_list. rtnl_lock ensures netdevices do
>not change during the critical section where a link is established.
>
>The lock order is consistent with other parts that touch netdevsim and
>should not deadlock.
>
>During nsim_dev_peer_read(), RCU read critical section ensures valid
>values even if stale.
>
>Signed-off-by: David Wei <dw@...idwei.uk>
>---
> drivers/net/netdevsim/dev.c | 134 +++++++++++++++++++++++++++---
> drivers/net/netdevsim/netdev.c | 6 ++
> drivers/net/netdevsim/netdevsim.h | 1 +
> 3 files changed, 128 insertions(+), 13 deletions(-)
>
>diff --git a/drivers/net/netdevsim/dev.c b/drivers/net/netdevsim/dev.c
>index 8d477aa99f94..6d5e4ce08dfd 100644
>--- a/drivers/net/netdevsim/dev.c
>+++ b/drivers/net/netdevsim/dev.c
>@@ -391,6 +391,124 @@ static const struct file_operations nsim_dev_rate_parent_fops = {
> .owner = THIS_MODULE,
> };
>
>+static struct nsim_dev *nsim_dev_find_by_id(unsigned int id)
>+{
>+ struct nsim_dev *dev;
>+
>+ list_for_each_entry(dev, &nsim_dev_list, list)
>+ if (dev->nsim_bus_dev->dev.id == id)
>+ return dev;
>+
>+ return NULL;
>+}
>+
>+static struct nsim_dev_port *
>+__nsim_dev_port_lookup(struct nsim_dev *nsim_dev, enum nsim_dev_port_type type,
>+ unsigned int port_index)
>+{
>+ struct nsim_dev_port *nsim_dev_port;
>+
>+ port_index = nsim_dev_port_index(type, port_index);
>+ list_for_each_entry(nsim_dev_port, &nsim_dev->port_list, list)
>+ if (nsim_dev_port->port_index == port_index)
>+ return nsim_dev_port;
>+ return NULL;
>+}
>+
>+static ssize_t nsim_dev_peer_read(struct file *file, char __user *data,
>+ size_t count, loff_t *ppos)
>+{
>+ struct nsim_dev_port *nsim_dev_port;
>+ struct netdevsim *peer;
>+ unsigned int id, port;
>+ ssize_t ret = 0;
>+ char buf[23];
>+
>+ nsim_dev_port = file->private_data;
>+ rcu_read_lock();
>+ peer = rcu_dereference(nsim_dev_port->ns->peer);
>+ if (!peer) {
>+ rcu_read_unlock();
>+ return 0;
>+ }
>+
>+ id = peer->nsim_bus_dev->dev.id;
>+ port = peer->nsim_dev_port->port_index;
>+ ret = scnprintf(buf, sizeof(buf), "%u %u\n", id, port);
>+ ret = simple_read_from_buffer(data, count, ppos, buf, ret);
>+
>+ rcu_read_unlock();
>+ return ret;
>+}
>+
>+static ssize_t nsim_dev_peer_write(struct file *file,
>+ const char __user *data,
>+ size_t count, loff_t *ppos)
>+{
>+ struct nsim_dev_port *nsim_dev_port, *peer_dev_port;
>+ struct nsim_dev *peer_dev;
>+ unsigned int id, port;
>+ char buf[22];
>+ ssize_t ret;
>+
>+ if (count >= sizeof(buf))
>+ return -ENOSPC;
>+
>+ ret = copy_from_user(buf, data, count);
>+ if (ret)
>+ return -EFAULT;
>+ buf[count] = '\0';
>+
>+ ret = sscanf(buf, "%u %u", &id, &port);
>+ if (ret != 2) {
>+ pr_err("Format is peer netdevsim \"id port\" (uint uint)\n");
>+ return -EINVAL;
>+ }
>+
>+ ret = -EINVAL;
>+ mutex_lock(&nsim_dev_list_lock);
>+ peer_dev = nsim_dev_find_by_id(id);
>+ if (!peer_dev) {
>+ pr_err("Peer netdevsim %u does not exist\n", id);
>+ goto out_mutex;
>+ }
>+
>+ devl_lock(priv_to_devlink(peer_dev));
Why exactly do you take devlink instance mutex of the peer here?
>+ rtnl_lock();
>+ nsim_dev_port = file->private_data;
>+ peer_dev_port = __nsim_dev_port_lookup(peer_dev, NSIM_DEV_PORT_TYPE_PF,
>+ port);
>+ if (!peer_dev_port) {
>+ pr_err("Peer netdevsim %u port %u does not exist\n", id, port);
>+ goto out_devl;
>+ }
>+
>+ if (nsim_dev_port == peer_dev_port) {
>+ pr_err("Cannot link netdevsim to itself\n");
>+ goto out_devl;
>+ }
>+
>+ rcu_assign_pointer(nsim_dev_port->ns->peer, peer_dev_port->ns);
>+ rcu_assign_pointer(peer_dev_port->ns->peer, nsim_dev_port->ns);
>+ ret = count;
>+
>+out_devl:
>+ rtnl_unlock();
>+ devl_unlock(priv_to_devlink(peer_dev));
>+out_mutex:
>+ mutex_unlock(&nsim_dev_list_lock);
>+
>+ return ret;
>+}
>+
>+static const struct file_operations nsim_dev_peer_fops = {
>+ .open = simple_open,
>+ .read = nsim_dev_peer_read,
>+ .write = nsim_dev_peer_write,
>+ .llseek = generic_file_llseek,
>+ .owner = THIS_MODULE,
>+};
>+
> static int nsim_dev_port_debugfs_init(struct nsim_dev *nsim_dev,
> struct nsim_dev_port *nsim_dev_port)
> {
>@@ -421,6 +539,9 @@ static int nsim_dev_port_debugfs_init(struct nsim_dev *nsim_dev,
> }
> debugfs_create_symlink("dev", nsim_dev_port->ddir, dev_link_name);
>
>+ debugfs_create_file("peer", 0600, nsim_dev_port->ddir,
>+ nsim_dev_port, &nsim_dev_peer_fops);
>+
> return 0;
> }
>
>@@ -1704,19 +1825,6 @@ void nsim_drv_remove(struct nsim_bus_dev *nsim_bus_dev)
> dev_set_drvdata(&nsim_bus_dev->dev, NULL);
> }
>
>-static struct nsim_dev_port *
>-__nsim_dev_port_lookup(struct nsim_dev *nsim_dev, enum nsim_dev_port_type type,
>- unsigned int port_index)
>-{
>- struct nsim_dev_port *nsim_dev_port;
>-
>- port_index = nsim_dev_port_index(type, port_index);
>- list_for_each_entry(nsim_dev_port, &nsim_dev->port_list, list)
>- if (nsim_dev_port->port_index == port_index)
>- return nsim_dev_port;
>- return NULL;
>-}
>-
> int nsim_drv_port_add(struct nsim_bus_dev *nsim_bus_dev, enum nsim_dev_port_type type,
> unsigned int port_index)
> {
>diff --git a/drivers/net/netdevsim/netdev.c b/drivers/net/netdevsim/netdev.c
>index aecaf5f44374..434322f6a565 100644
>--- a/drivers/net/netdevsim/netdev.c
>+++ b/drivers/net/netdevsim/netdev.c
>@@ -388,6 +388,7 @@ nsim_create(struct nsim_dev *nsim_dev, struct nsim_dev_port *nsim_dev_port)
> ns->nsim_dev = nsim_dev;
> ns->nsim_dev_port = nsim_dev_port;
> ns->nsim_bus_dev = nsim_dev->nsim_bus_dev;
>+ RCU_INIT_POINTER(ns->peer, NULL);
> SET_NETDEV_DEV(dev, &ns->nsim_bus_dev->dev);
> SET_NETDEV_DEVLINK_PORT(dev, &nsim_dev_port->devlink_port);
> nsim_ethtool_init(ns);
>@@ -407,8 +408,13 @@ nsim_create(struct nsim_dev *nsim_dev, struct nsim_dev_port *nsim_dev_port)
> void nsim_destroy(struct netdevsim *ns)
> {
> struct net_device *dev = ns->netdev;
>+ struct netdevsim *peer;
>
> rtnl_lock();
>+ peer = rtnl_dereference(ns->peer);
>+ if (peer)
>+ RCU_INIT_POINTER(peer->peer, NULL);
>+ RCU_INIT_POINTER(ns->peer, NULL);
> unregister_netdevice(dev);
> if (nsim_dev_port_is_pf(ns->nsim_dev_port)) {
> nsim_macsec_teardown(ns);
>diff --git a/drivers/net/netdevsim/netdevsim.h b/drivers/net/netdevsim/netdevsim.h
>index babb61d7790b..24fc3fbda791 100644
>--- a/drivers/net/netdevsim/netdevsim.h
>+++ b/drivers/net/netdevsim/netdevsim.h
>@@ -125,6 +125,7 @@ struct netdevsim {
> } udp_ports;
>
> struct nsim_ethtool ethtool;
>+ struct netdevsim __rcu *peer;
> };
>
> struct netdevsim *
>--
>2.39.3
>
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