Revert "nvme-tcp: lockdep: use dynamic lockdep keys per socket instance"

This reverts commit 19bdb70c77d3b24239a453291299b64040bdba86.

The commit 19bdb70c77d3 ("nvme-tcp: lockdep: use dynamic lockdep keys
per socket instance") addressed the lockdep WARN caused by the circular
lock dependency among six locks:

  set->srcu -> sk_lock -> cpu_hotplug_lock -> fs_reclaim -> q_usage_counter -> elevator_lock -> set->srcu

As its title says, the commit cut the dependency by introducing the
dynamic lockdep keys per socket instance. However, as described in the
Link tag URL, the commit made a wrong assumption: it assumed that
__fput_sync(queue->sock->file) in nvme_tcp_free_queue() would
synchronously destroy the socket. This is wrong: when in-flight packets
cause delayed free of the socket, the prematurely freed lockdep key is
referred to and causes another WARN. The commit is an imperfect fix.
Hence revert it.

To address the circular dependency among the six locks, another solution
is required. It is provided by the commit 0ba6912f7e97 ("Revert "once:
don't use a work queue to reset sleepable static key""). It cuts the
dependency between sk_lock and cpu_hotplug_lock. This solution is
simpler, and reduces the complexity in nvme-tcp.

Link: https://lore.kernel.org/lkml/CANn89i+wnTLC==UnXCpjsS4YxvEfhe5oK0N7fttbqr1zKyqdug@mail.gmail.com/
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>

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