[net PATCH 4/4] net: ethtool: keep rtnl_lock for the ioctl self test

From: Alexander Duyck <alexanderduyck@fb.com>

fbnic's offline self test brings the interface down and back up with
netif_close() / netif_open(), both of which require rtnl_lock. Since the
ethtool IOCTL path became rtnl-optional for ops-locked drivers, the
ETHTOOL_TEST ioctl runs holding only the netdev instance lock, so on an
ops-locked driver (fbnic is ops-locked via queue_mgmt_ops) the self test
now tears the device down without rtnl_lock.

With lockdep this reproduces deterministically on every offline self
test; note the sole lock held is the instance lock, not rtnl:

  WARNING: suspicious RCU usage
  net/core/netpoll.c:207 suspicious rcu_dereference_protected() usage!
  1 lock held by ethtool/107:
   #0: (&dev->lock){+.+.}, at: dev_ethtool
  Call Trace:
   netpoll_poll_disable
   __dev_close_many
   netif_close_many
   netif_close
   fbnic_self_test
   dev_ethtool_locked
   dev_ethtool
   dev_ioctl
   sock_ioctl
   __x64_sys_ioctl

Without lockdep the same condition trips ASSERT_RTNL() in
__dev_close_many() / __dev_open(); that check only samples the global
rtnl state, so it can be masked by a concurrent rtnl holder, but the
device is still being reconfigured without the lock it requires.

self_test is a legacy ioctl-only command, so an ETHTOOL_TEST case is
only needed on the ioctl path. Add an opt-in bit for drivers whose
self test needs rtnl_lock and set it on fbnic.

Fixes: f994752b1127 ("net: ethtool: optionally skip rtnl_lock on IOCTL path")
Signed-off-by: Alexander Duyck <alexanderduyck@fb.com>
---
 drivers/net/ethernet/meta/fbnic/fbnic_ethtool.c |    3 ++-
 include/linux/ethtool.h                         |    2 ++
 net/ethtool/common.h                            |    2 ++
 3 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/meta/fbnic/fbnic_ethtool.c b/drivers/net/ethernet/meta/fbnic/fbnic_ethtool.c
index 0e47088ec44b..423f179c9d47 100644
--- a/drivers/net/ethernet/meta/fbnic/fbnic_ethtool.c
+++ b/drivers/net/ethernet/meta/fbnic/fbnic_ethtool.c

@@ -2025,7 +2025,8 @@ static const struct ethtool_ops fbnic_ethtool_ops = {
 					  ETHTOOL_OP_NEEDS_RTNL_SPAUSEPARAM |
 					  ETHTOOL_OP_NEEDS_RTNL_SCHANNELS |
 					  ETHTOOL_OP_NEEDS_RTNL_SRINGPARAM |
-					  ETHTOOL_OP_NEEDS_RTNL_GLINK,
+					  ETHTOOL_OP_NEEDS_RTNL_GLINK |
+					  ETHTOOL_OP_NEEDS_RTNL_TEST,
 	.get_drvinfo			= fbnic_get_drvinfo,
 	.get_regs_len			= fbnic_get_regs_len,
 	.get_regs			= fbnic_get_regs,

diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
index 12683b5d125e..97a1adbd9eae 100644
--- a/include/linux/ethtool.h
+++ b/include/linux/ethtool.h

@@ -944,6 +944,7 @@ struct kernel_ethtool_ts_info {
 #define ETHTOOL_OP_NEEDS_RTNL_SPAUSEPARAM	BIT(6)
 #define ETHTOOL_OP_NEEDS_RTNL_RSS		BIT(7)
 #define ETHTOOL_OP_NEEDS_RTNL_GLINK		BIT(8)
+#define ETHTOOL_OP_NEEDS_RTNL_TEST		BIT(9)
 
 /**
  * struct ethtool_ops - optional netdev operations

@@ -981,6 +982,7 @@ struct kernel_ethtool_ts_info {
  *	 - netdev_update_features()
  *	 - netif_set_real_num_tx_queues()
  *	 - ethtool_op_get_link() (syncs link watch under rtnl_lock)
+ *	 - netif_open() / netif_close() (used by @self_test)
  *
  * @get_drvinfo: Report driver/device information. Modern drivers no
  *	longer have to implement this callback. Most fields are

diff --git a/net/ethtool/common.h b/net/ethtool/common.h
index 4e5356e26f40..ae32e7fdb563 100644
--- a/net/ethtool/common.h
+++ b/net/ethtool/common.h

@@ -163,6 +163,8 @@ ethtool_ioctl_needs_rtnl(const struct net_device *dev, u32 ethcmd)
 		return ops->op_needs_rtnl & ETHTOOL_OP_NEEDS_RTNL_RSS;
 	case ETHTOOL_GLINK:
 		return ops->op_needs_rtnl & ETHTOOL_OP_NEEDS_RTNL_GLINK;
+	case ETHTOOL_TEST:
+		return ops->op_needs_rtnl & ETHTOOL_OP_NEEDS_RTNL_TEST;
 	}
 	return false;
 }