[net PATCH v2 1/6] net: ethtool: keep rtnl_lock for the ioctl self test

From: Alexander Duyck <alexanderduyck@fb.com>

An offline self test that brings the interface down and back up with
netif_close() / netif_open() requires rtnl_lock for both. 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 the self test now tears the device down without
rtnl_lock.

With lockdep this reproduces deterministically on every offline self
test on such a driver; 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.

The ethtool 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 the ops-locked drivers whose
offline self test tears the interface down and up:

  - fbnic (ops-locked via queue_mgmt_ops): fbnic_self_test() offline path
    uses netif_close() / netif_open().
  - bnxt (ops-locked via queue_mgmt_ops): bnxt_self_test() offline path
    goes through bnxt_close_nic() / bnxt_half_open_nic() /
    bnxt_half_close_nic() / bnxt_open_nic(), which close and reopen the
    device.

Fixes: f994752b1127 ("net: ethtool: optionally skip rtnl_lock on IOCTL path")
Signed-off-by: Alexander Duyck <alexanderduyck@fb.com>
---
 drivers/net/ethernet/broadcom/bnxt/bnxt_ethtool.c |    3 ++-
 drivers/net/ethernet/meta/fbnic/fbnic_ethtool.c   |    3 ++-
 include/linux/ethtool.h                           |    2 ++
 net/ethtool/common.h                              |    2 ++
 4 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/net/ethernet/broadcom/bnxt/bnxt_ethtool.c b/drivers/net/ethernet/broadcom/bnxt/bnxt_ethtool.c
index 62bc9cae613c..622e89587e5d 100644
--- a/drivers/net/ethernet/broadcom/bnxt/bnxt_ethtool.c
+++ b/drivers/net/ethernet/broadcom/bnxt/bnxt_ethtool.c

@@ -5733,7 +5733,8 @@ const struct ethtool_ops bnxt_ethtool_ops = {
 	.op_needs_rtnl			= ETHTOOL_OP_NEEDS_RTNL_SCHANNELS |
 					  ETHTOOL_OP_NEEDS_RTNL_SRINGPARAM |
 					  ETHTOOL_OP_NEEDS_RTNL_SCOALESCE |
-					  ETHTOOL_OP_NEEDS_RTNL_RSS,
+					  ETHTOOL_OP_NEEDS_RTNL_RSS |
+					  ETHTOOL_OP_NEEDS_RTNL_TEST,
 	.supported_coalesce_params = ETHTOOL_COALESCE_USECS |
 				     ETHTOOL_COALESCE_MAX_FRAMES |
 				     ETHTOOL_COALESCE_USECS_IRQ |

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 253600c0eccd..c4c9ce038611 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;
 }