Merge branch 'net-add-preliminary-netdev-refcount-tracking'

Eric Dumazet says:

====================
net: add preliminary netdev refcount tracking

Two first patches add a generic infrastructure, that will be used
to get tracking of refcount increments/decrements.

The general idea is to be able to precisely pair each decrement with
a corresponding prior increment. Both share a cookie, basically
a pointer to private data storing stack traces.

The third patch adds dev_hold_track() and dev_put_track() helpers
(CONFIG_NET_DEV_REFCNT_TRACKER)

Then a series of 20 patches converts some dev_hold()/dev_put()
pairs to new hepers : dev_hold_track() and dev_put_track().

Hopefully this will be used by developpers and syzbot to
root cause bugs that cause netdevice dismantles freezes.

With CONFIG_PCPU_DEV_REFCNT=n option, we were able to detect
some class of bugs, but too late (when too many dev_put()
were happening).

Another series will be sent after this one is merged.

v3: moved NET_DEV_REFCNT_TRACKER to net/Kconfig.debug
    added "depends on DEBUG_KERNEL && STACKTRACE_SUPPORT"
    to hopefully get rid of kbuild reports for ARCH=nios2
    Reworded patch 3 changelog.
    Added missing htmldocs (Jakub)

v2: added four additional patches,
    added netdev_tracker_alloc() and netdev_tracker_free()
    addressed build error (kernel bots),
    use GFP_ATOMIC in test_ref_tracker_timer_func()
====================

Link: https://lore.kernel.org/r/20211205042217.982127-1-eric.dumazet@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>