Merge branch 'bpf: Remove recursion check for struct_ops prog'

Martin KaFai Lau says:

====================

From: Martin KaFai Lau <martin.lau@kernel.org>

The struct_ops is sharing the tracing-trampoline's enter/exit
function which tracks prog->active to avoid recursion.  It turns
out the struct_ops bpf prog will hit this prog->active and
unnecessarily skipped running the struct_ops prog.  eg.  The
'.ssthresh' may run in_task() and then interrupted by softirq
that runs the same '.ssthresh'.

The kernel does not call the tcp-cc's ops in a recursive way,
so this set is to remove the recursion check for struct_ops prog.

v3:
- Clear the bpf_chg_cc_inprogress from the newly cloned tcp_sock
  in tcp_create_openreq_child() because the listen sk can
  be cloned without lock being held. (Eric Dumazet)

v2:
- v1 [0] turned into a long discussion on a few cases and also
  whether it needs to follow the bpf_run_ctx chain if there is
  tracing bpf_run_ctx (kprobe/trace/trampoline) running in between.

  It is a good signal that it is not obvious enough to reason
  about it and needs a tradeoff for a more straight forward approach.

  This revision uses one bit out of an existing 1 byte hole
  in the tcp_sock.  It is in Patch 4.

  [0]: https://lore.kernel.org/bpf/20220922225616.3054840-1-kafai@fb.com/T/#md98d40ac5ec295fdadef476c227a3401b2b6b911
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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