blktests nvme/062 lockdep — defer TLS inline send to io_work?

[Xixin Liu]

Hi,

I'm looking at the nvme/062 failure Shinichiro reported on linux-7.1.y
(PROVE_LOCKING=y, blktests v5a62429536b1) and would like to sanity-check
a fix direction before sending a formal patch.

Link: https://lore.kernel.org/linux-nvme/ajtk1CaN1pBreS4O@shinmob/T/

Problem (reproduced on linux-next, same test)
---------------------------------------------
With PROVE_LOCKING=y, nvme/062 (TLS connect) fails with dmesg:

  WARNING: possible circular locking dependency detected
  ...
  tx_lock (tls_sw_sendmsg)
  ...
  &set->srcu (blk_mq / kblockd context)

The #0 stack is nvme_tcp_queue_request() doing an inline nvme_tcp_send_all()
from queue_rq, which calls tls_sw_sendmsg() while blk_mq still holds srcu.
Lockdep already knows tx_lock -> elevator_lock -> srcu, so the reverse
order triggers the cycle.

Teardown fixes (__fput_sync, memalloc_noio_save, 26bb12b9caaf) are already
present in current trees; 062 still fails — this looks like the TLS send
path on top of blk_mq, not the disconnect/teardown chain.

Proposed fix (one line + comment)
---------------------------------
Skip the queue_rq inline-send optimization when nvme_tcp_queue_tls(queue):

  if (queue->io_cpu == raw_smp_processor_id() &&
      !nvme_tcp_queue_tls(queue) &&
      empty && mutex_trylock(&queue->send_mutex)) {
          nvme_tcp_send_all(queue);
          ...
  }

TLS traffic would always go through nvme_tcp_io_work on nvme_tcp_wq (same
as write_space / backpressure paths already do).  Lab check: nvme/062
passes, no lockdep splat in dmesg.

Does skipping inline send for TLS queues (plain TCP unchanged) look like a
reasonable fix to you?  I can post [PATCH] if this direction sounds OK.

Thanks,
Xixin Liu