netdev - [PATCH net-next 0/4] improve ethtool/rtnl vs devlink locking

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Date:   Fri, 29 Oct 2021 21:06:07 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     davem@...emloft.net
Cc:     netdev@...r.kernel.org, jiri@...nulli.us, leon@...nel.org,
        mkubecek@...e.cz, andrew@...n.ch, f.fainelli@...il.com,
        Jakub Kicinski <kuba@...nel.org>
Subject: [PATCH net-next 0/4] improve ethtool/rtnl vs devlink locking

During ethtool netlink development we decided to move some of
the commmands to devlink. Since we don't want drivers to implement
both devlink and ethtool version of the commands ethtool ioctl
falls back to calling devlink. Unfortunately devlink locks must
be taken before rtnl_lock. This results in a questionable
dev_hold() / rtnl_unlock() / devlink / rtnl_lock() / dev_put()
pattern.

This method "works" but it working depends on drivers in question
not doing much in ethtool_ops->begin / complete, and on the netdev
not having needs_free_netdev set.

Since commit 437ebfd90a25 ("devlink: Count struct devlink consumers")
we can hold a reference on a devlink instance and prevent it from
going away (sort of like netdev with dev_hold()). We can use this
to create a more natural reference nesting where we get a ref on
the devlink instance and make the devlink call entirely outside
of the rtnl_lock section.

Jakub Kicinski (4):
  ethtool: push the rtnl_lock into dev_ethtool()
  ethtool: handle info/flash data copying outside rtnl_lock
  devlink: expose get/put functions
  ethtool: don't drop the rtnl_lock half way thru the ioctl

 include/net/devlink.h |  16 ++++-
 net/core/dev_ioctl.c  |   2 -
 net/core/devlink.c    |  53 ++++-----------
 net/ethtool/ioctl.c   | 148 ++++++++++++++++++++++++++++++------------
 4 files changed, 134 insertions(+), 85 deletions(-)

-- 
2.31.1