On Fri, 28 Jun 2019 12:40:29 -0700, John Fastabend wrote:

The lock() is already held when entering unhash() side so need to
handle this case as well,

CPU 0 (free)          CPU 1 (wq)

lock(sk)              ctx = tls_get_ctx(sk) <- need to be check null ptr
sk_prot->unhash()
  set_bit()
  cancel_work()
  ...
  kfree(ctx)
unlock(sk)

but using cancel and doing an unlikely(!ctx) check should be
sufficient to handle wq. 

I'm not sure we can kfree ctx, the work struct itself is in it, no?

What I'm not sure how to solve now is
in patch 2 of this series unhash is still calling strp_done
with the sock lock. Maybe we need to do a deferred release
like sockmap side?

Right, we can't do anything that sleeps in unhash, since we're holding
the spinlock there, not the "owner" lock.

Trying to drop the lock and then grabbing it again doesn't
seem right to me seems based on comment in tcp_abort we
could potentially "race with userspace socket closes such
as tcp_close". iirc I think one of the tls splats from syzbot
looked something like this may have happened.

For now I'm considering adding a strp_cancel() op. Seeing
we are closing() the socket and tearkng down we can probably
be OK with throwing out strp results.

But don't we have to flush the work queues before we free ctx?  We'd
need to alloc a workqueue and schedule a work to flush the other works
and then free?

Why can't tls sockets exist outside of established state?  If shutdown
doesn't call close, perhaps we can add a shutdown callback?  It doesn't
seem to be called from BH?

Sorry for all the questions, I'm not really able to fully wrap my head
around this. I also feel like I'm missing the sockmap piece that may
be why you prefer unhash over disconnect.

FWIW Davide's ULP diag support patches will require us to most likely
free ctx with kfree_rcu(). diag only has a ref on struct sock, so if 
we want to access ctx we need RCU or to lock every socket. It's a
little bit of an abuse of RCU, because the data under our feet may
actually change, but the fields we dump will only get inited once
after ulp is installed.