On Tue, Feb 26, 2019 at 03:31:32PM +0000, Rainer Weikusat wrote: > Al Viro <v...@zeniv.linux.org.uk> writes: > > On Tue, Feb 26, 2019 at 06:28:17AM +0000, Al Viro wrote: > > [...] > > > >> * if after relocking we see that unix_peer(sk) now > >> is equal to other, we arrange for wakeup forwarding from other's > >> peer_wait *and* if that has (likely) succeeded we fail with -EAGAIN. > >> Huh? > > This returns 1 if sending isn't possible at the moment, ie, if the > process which tries to send has to wait.
Except that in _this_ case we won't be waiting at all - we'll just return -EAGAIN (as one could expect, what with no timeout given/left). So what's the point of forwarding wakeups? IOW, what is it that we expect to be waiting on sk_sleep(sk)? Note that it won't be this call of sendmsg(2) (it'll bugger off without any further waiting). It won't be subsequent calls of sendmsg(2) either - they either sleep on skb allocation (which has nothing to do with destination) _or_ they sleep directly on other->peer_wait. And poll(), while it will be sleeping on sk_sleep(sk), will make sure to set the forwarding up. I understand what the unix_dgram_peer_wake_me() is doing; I understand what unix_dgram_poll() is using it for. What I do not understand is what's the point of doing that in unix_dgram_sendmsg()...
