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Message-ID: <alpine.DEB.2.21.1907021450320.5764@ramsan.of.borg>
Date: Tue, 2 Jul 2019 14:54:49 +0200 (CEST)
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Mahesh Bandewar <maheshb@...gle.com>
cc: Netdev <netdev@...r.kernel.org>,
Eric Dumazet <edumazet@...gle.com>,
David Miller <davem@...emloft.net>,
Michael Chan <michael.chan@...adcom.com>,
Daniel Axtens <dja@...ens.net>,
Mahesh Bandewar <mahesh@...dewar.net>,
"Paul E. McKenney" <paulmck@...ux.ibm.com>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: suspicious RCU usage (was: Re: [PATCHv3 next 1/3] loopback: create
blackhole net device similar to loopack.)
Hi Mahesh,
On Mon, 1 Jul 2019, Mahesh Bandewar wrote:
> Create a blackhole net device that can be used for "dead"
> dst entries instead of loopback device. This blackhole device differs
> from loopback in few aspects: (a) It's not per-ns. (b) MTU on this
> device is ETH_MIN_MTU (c) The xmit function is essentially kfree_skb().
> and (d) since it's not registered it won't have ifindex.
>
> Lower MTU effectively make the device not pass the MTU check during
> the route check when a dst associated with the skb is dead.
>
> Signed-off-by: Mahesh Bandewar <maheshb@...gle.com>
This is now commit 4de83b88c66a1e4d ("loopback: create blackhole net
device similar to loopack.") in net-next, and causes the following
warning on arm64:
WARNING: suspicious RCU usage
5.2.0-rc6-arm64-renesas-01699-g4de83b88c66a1e4d #263 Not tainted
-----------------------------
include/linux/rtnetlink.h:85 suspicious rcu_dereference_protected() usage!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1
no locks held by swapper/0/1.
stack backtrace:
CPU: 2 PID: 1 Comm: swapper/0 Not tainted 5.2.0-rc6-arm64-renesas-01699-g4de83b88c66a1e4d #263
Hardware name: Renesas Salvator-X 2nd version board based on r8a7795 ES2.0+ (DT)
Call trace:
dump_backtrace+0x0/0x148
show_stack+0x14/0x20
dump_stack+0xd4/0x11c
lockdep_rcu_suspicious+0xcc/0x110
dev_init_scheduler+0x114/0x150
blackhole_netdev_init+0x40/0x80
do_one_initcall+0x178/0x37c
kernel_init_freeable+0x490/0x530
kernel_init+0x10/0x100
ret_from_fork+0x10/0x1c
> ---
> v1->v2->v3
> no change
>
> drivers/net/loopback.c | 76 ++++++++++++++++++++++++++++++++++-----
> include/linux/netdevice.h | 2 ++
> 2 files changed, 69 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/net/loopback.c b/drivers/net/loopback.c
> index 87d361666cdd..3b39def5471e 100644
> --- a/drivers/net/loopback.c
> +++ b/drivers/net/loopback.c
> @@ -55,6 +55,13 @@
> #include <net/net_namespace.h>
> #include <linux/u64_stats_sync.h>
>
> +/* blackhole_netdev - a device used for dsts that are marked expired!
> + * This is global device (instead of per-net-ns) since it's not needed
> + * to be per-ns and gets initialized at boot time.
> + */
> +struct net_device *blackhole_netdev;
> +EXPORT_SYMBOL(blackhole_netdev);
> +
> /* The higher levels take care of making this non-reentrant (it's
> * called with bh's disabled).
> */
> @@ -150,12 +157,14 @@ static const struct net_device_ops loopback_ops = {
> .ndo_set_mac_address = eth_mac_addr,
> };
>
> -/* The loopback device is special. There is only one instance
> - * per network namespace.
> - */
> -static void loopback_setup(struct net_device *dev)
> +static void gen_lo_setup(struct net_device *dev,
> + unsigned int mtu,
> + const struct ethtool_ops *eth_ops,
> + const struct header_ops *hdr_ops,
> + const struct net_device_ops *dev_ops,
> + void (*dev_destructor)(struct net_device *dev))
> {
> - dev->mtu = 64 * 1024;
> + dev->mtu = mtu;
> dev->hard_header_len = ETH_HLEN; /* 14 */
> dev->min_header_len = ETH_HLEN; /* 14 */
> dev->addr_len = ETH_ALEN; /* 6 */
> @@ -174,11 +183,20 @@ static void loopback_setup(struct net_device *dev)
> | NETIF_F_NETNS_LOCAL
> | NETIF_F_VLAN_CHALLENGED
> | NETIF_F_LOOPBACK;
> - dev->ethtool_ops = &loopback_ethtool_ops;
> - dev->header_ops = ð_header_ops;
> - dev->netdev_ops = &loopback_ops;
> + dev->ethtool_ops = eth_ops;
> + dev->header_ops = hdr_ops;
> + dev->netdev_ops = dev_ops;
> dev->needs_free_netdev = true;
> - dev->priv_destructor = loopback_dev_free;
> + dev->priv_destructor = dev_destructor;
> +}
> +
> +/* The loopback device is special. There is only one instance
> + * per network namespace.
> + */
> +static void loopback_setup(struct net_device *dev)
> +{
> + gen_lo_setup(dev, (64 * 1024), &loopback_ethtool_ops, ð_header_ops,
> + &loopback_ops, loopback_dev_free);
> }
>
> /* Setup and register the loopback device. */
> @@ -213,3 +231,43 @@ static __net_init int loopback_net_init(struct net *net)
> struct pernet_operations __net_initdata loopback_net_ops = {
> .init = loopback_net_init,
> };
> +
> +/* blackhole netdevice */
> +static netdev_tx_t blackhole_netdev_xmit(struct sk_buff *skb,
> + struct net_device *dev)
> +{
> + kfree_skb(skb);
> + net_warn_ratelimited("%s(): Dropping skb.\n", __func__);
> + return NETDEV_TX_OK;
> +}
> +
> +static const struct net_device_ops blackhole_netdev_ops = {
> + .ndo_start_xmit = blackhole_netdev_xmit,
> +};
> +
> +/* This is a dst-dummy device used specifically for invalidated
> + * DSTs and unlike loopback, this is not per-ns.
> + */
> +static void blackhole_netdev_setup(struct net_device *dev)
> +{
> + gen_lo_setup(dev, ETH_MIN_MTU, NULL, NULL, &blackhole_netdev_ops, NULL);
> +}
> +
> +/* Setup and register the blackhole_netdev. */
> +static int __init blackhole_netdev_init(void)
> +{
> + blackhole_netdev = alloc_netdev(0, "blackhole_dev", NET_NAME_UNKNOWN,
> + blackhole_netdev_setup);
> + if (!blackhole_netdev)
> + return -ENOMEM;
> +
> + dev_init_scheduler(blackhole_netdev);
> + dev_activate(blackhole_netdev);
> +
> + blackhole_netdev->flags |= IFF_UP | IFF_RUNNING;
> + dev_net_set(blackhole_netdev, &init_net);
> +
> + return 0;
> +}
> +
> +device_initcall(blackhole_netdev_init);
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index eeacebd7debb..88292953aa6f 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -4870,4 +4870,6 @@ do { \
> #define PTYPE_HASH_SIZE (16)
> #define PTYPE_HASH_MASK (PTYPE_HASH_SIZE - 1)
>
> +extern struct net_device *blackhole_netdev;
> +
> #endif /* _LINUX_NETDEVICE_H */
>
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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