tipc: fix race/inefficiencies in poll/wait behaviour
When an application blocks at poll/select on a TIPC socket while requesting a specific event mask, both the filter_rcv() and wakeupdispatch() case will wake it up unconditionally whenever the state changes (i.e an incoming message arrives, or congestion has subsided). No mask is used. To avoid this, we populate sk->sk_data_ready and sk->sk_write_space with tipc_data_ready and tipc_write_space respectively, which makes tipc more in alignment with the rest of the networking code. These pass the exact set of possible events to the waker in fs/select.c hence avoiding waking up blocked processes unnecessarily. In doing so, we uncover another issue -- that there needs to be a memory barrier in these poll/receive callbacks, otherwise we are subject to the the same race as documented above wq_has_sleeper() [in commit a57de0b4 "net: adding memory barrier to the poll and receive callbacks"]. So we need to replace poll_wait() with sock_poll_wait() and use rcu protection for the sk->sk_wq pointer in these two new functions. Signed-off-by: NYing Xue <ying.xue@windriver.com> Signed-off-by: NPaul Gortmaker <paul.gortmaker@windriver.com>
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