Re: [PATCH v1 net-next 06/12] af_unix: Reuse out_pipe label in unix_stream_sendmsg().

[Joe Damato <jdamato@fastly.com>]

On Sat, Jan 11, 2025 at 12:22:31AM +0900, Kuniyuki Iwashima wrote:
> From: Simon Horman <horms@kernel.org>
> Date: Fri, 10 Jan 2025 11:43:44 +0000
> > On Fri, Jan 10, 2025 at 06:26:35PM +0900, Kuniyuki Iwashima wrote:
> > > This is a follow-up of commit d460b04bc452 ("af_unix: Clean up
> > > error paths in unix_stream_sendmsg().").
> > > 
> > > If we initialise skb with NULL in unix_stream_sendmsg(), we can
> > > reuse the existing out_pipe label for the SEND_SHUTDOWN check.
> > > 
> > > Let's rename do it and adjust the existing label as out_pipe_lock.
> > > 
> > > While at it, size and data_len are moved to the while loop scope.
> > > 
> > > Suggested-by: Paolo Abeni <pabeni@redhat.com>
> > > Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
> > > ---
> > >  net/unix/af_unix.c | 23 +++++++++--------------
> > >  1 file changed, 9 insertions(+), 14 deletions(-)
> > > 
> > > diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> > > index b190ea8b8e9d..6505eeab9957 100644
> > > --- a/net/unix/af_unix.c
> > > +++ b/net/unix/af_unix.c
> > 
> > ...
> > 
> > > @@ -2285,16 +2283,12 @@ static int unix_stream_sendmsg(struct socket *sock, struct msghdr *msg,
> > >  		}
> > >  	}
> > >  
> > > -	if (READ_ONCE(sk->sk_shutdown) & SEND_SHUTDOWN) {
> > > -		if (!(msg->msg_flags & MSG_NOSIGNAL))
> > > -			send_sig(SIGPIPE, current, 0);
> > > -
> > > -		err = -EPIPE;
> > > -		goto out_err;
> > > -	}
> > > +	if (READ_ONCE(sk->sk_shutdown) & SEND_SHUTDOWN)
> > 
> > Hi Iwashima-san,
> > 
> > I think you need to set reason here.
> > 
> > Flagged by W=1 builds with clang-19.
> 
> Hi Simon,
> 
> I didn't set it here because skb == NULL and kfree_skb()
> doesn't touch reason, and KMSAN won't complain about uninit.
> 
> Should I use SKB_NOT_DROPPED_YET or drop patch 6 or leave
> it as is ?
> 
> What do you think ?

My vote is that SKB_NOT_DROPPED_YET is not appropriate here.

Maybe SKB_DROP_REASON_SOCKET_CLOSE since it is in SEND_SHUTDOWN
state?