net: ethtool: optionally skip rtnl_lock on IOCTL path

Convert the IOCTL path similarly to how we converted Netlink.
The device lookup gets a little hairy. We could take rtnl_lock
unconditionally and drop it before calling the driver (this would
avoid the reference + liveness check). But I think being able
to make progress even if rtnl is dead-locked is quite useful.

First extra concern is handling features. List all the cmds which
modify features and always take rtnl_lock. We could fold this list
into ethtool_ioctl_needs_rtnl() but seems cleaner to keep
ethtool_ioctl_needs_rtnl() driver-related. If a driver changed
features and we were not holding rtnl_lock - warn about it.
It can only happen on buggy ops locked drivers (buggy because
they should have set appropriate "I need rtnl for op X" bit).

Second wrinkle is the PHY ID hack which drops the locks while
sleeping. Convert its static "busy" variable which used to
be protected by rtnl_lock to a field in struct ethtool_netdev_state.
This feature is about identifying an adapter or a port within
a system, so being able to blink multiple LEDs at the same
time is likely not very useful in practice. But it's the simplest
fix, we can add a mutex if someone thinks a system should only
be ID'ing one port at a time.

Reviewed-by: Eric Dumazet <edumazet@google.com>
Acked-by: Stanislav Fomichev <sdf@fomichev.me>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://patch.msgid.link/20260605002912.3456868-12-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
index 74c8109b0cf3..da29017c757f 100644
--- a/include/linux/ethtool.h
+++ b/include/linux/ethtool.h
@@ -1375,6 +1375,7 @@ int ethtool_virtdev_set_link_ksettings(struct net_device *dev,
  *			within RTNL.
  * @rss_indir_user_size: Number of user provided entries for the default
  *			 (context 0) indirection table.
+ * @phys_id_busy:	Loop blinking the device LED is running.
  * @wol_enabled:	Wake-on-LAN is enabled
  * @module_fw_flash_in_progress: Module firmware flashing is in progress.
  */
@@ -1382,6 +1383,7 @@ struct ethtool_netdev_state {
 	struct xarray		rss_ctx;
 	struct mutex		rss_lock;
 	u32			rss_indir_user_size;
+	unsigned		phys_id_busy:1;
 	unsigned		wol_enabled:1;
 	unsigned		module_fw_flash_in_progress:1;
 };