Re: [PATCH net 4/4] net/smc: Fix wq mismatch issue caused by smc fallback

On 27/10/2021 10:52, Tony Lu wrote:

From: Wen Gu <guwen@linux.alibaba.com>

A socket_wq mismatch issue may occur because of fallback.

When use SMC to replace TCP, applications add an epoll entry into SMC
socket's wq, but kernel uses clcsock's wq instead of SMC socket's wq
once fallback occurs, which means the application's epoll fd dosen't
work anymore.

I am not sure if I understand this fix completely, please explain your intentions
for the changes in more detail.

What I see so far:
- smc_create() swaps the sk->sk_wq of the clcsocket and the new SMC socket
  - sets clcsocket sk->sk_wq to smcsocket->wq (why?)
  - sets smcsocket sk->sk_wq to clcsocket->wq (why?)
- smc_switch_to_fallback() resets the clcsock sk->sk_wq to clcsocket->wq
- smc_accept() sets smcsocket sk->sk_wq to clcsocket->wq when it is NOT fallback
  - but this was already done before in smc_create() ??
- smc_poll() now always uses clcsocket->wq for the call to sock_poll_wait()

In smc_poll() the comment says that now clcsocket->wq is used for poll, whats
the relation between socket->wq and socket->sk->sk_wq here?