On Thu, Jul 24, 2025 at 03:45:28PM +0300, Vitaliy Makkoveev wrote:
> While calling soreadable() from filt_soread(), the `so_qlen' is already
> loaded to local `qlen' and used as "rv = qlen || soreadable(so)" for
> return value. Currently this path of filt_soread() is locked with
> solock(), so if `so_qlen' is null the second load within soreadable()
> only consumes CPU cycles. But in hypothetically unlocked filt_soread()
> the "rv = qlen || soreadable(so)" is inconsistent. We already did some
> movements to call filt_soread() without socket lock, so adjust
> soreadable() for that.
> 
> Except the filt_soread(), the only caller of soreadable() is
> sounsplice(). Since the socket could became listening and have some
> pending connections, do the `so_qlen' load together with soreadable().

sosplice() does not allow SO_ACCEPTCONN sockets.
solisten() does not allow isspliced(so) || issplicedback(so) sockets.

The change in sounsplice() is not necessary and confusing, so->so_qlen
cannot happen.

> Note, for this release cycle I want to keep filt_soread() locked. Also,
> soreadable() does `so_error' load which is already loaded in the
> beginning of filt_soread(). We don't use this value in the SO_ACCEPTCONN
> path, so this load could be moved to the SS_CANTRCVMORE path there this
> value actually used, but this is not related to this diff.
> 
> ok?

OK bluhm@ for the second chunk in soreadable().

> Index: sys/kern/uipc_socket.c
> ===================================================================
> RCS file: /cvs/src/sys/kern/uipc_socket.c,v
> diff -u -p -r1.383 uipc_socket.c
> --- sys/kern/uipc_socket.c	23 Jul 2025 20:18:04 -0000	1.383
> +++ sys/kern/uipc_socket.c	24 Jul 2025 12:02:00 -0000
> @@ -1458,7 +1458,7 @@ sounsplice(struct socket *so, struct soc
>  
>  		solock_shared(so);
>  		mtx_enter(&so->so_rcv.sb_mtx);
> -		readable = soreadable(so);
> +		readable = so->so_qlen || soreadable(so);
>  		mtx_leave(&so->so_rcv.sb_mtx);
>  		if (readable)
>  			sorwakeup(so);
> Index: sys/sys/socketvar.h
> ===================================================================
> RCS file: /cvs/src/sys/sys/socketvar.h,v
> diff -u -p -r1.158 socketvar.h
> --- sys/sys/socketvar.h	8 Apr 2025 15:31:22 -0000	1.158
> +++ sys/sys/socketvar.h	24 Jul 2025 12:02:00 -0000
> @@ -387,7 +387,7 @@ soreadable(struct socket *so)
>  	soassertlocked_readonly(so);
>  	if (isspliced(so))
>  		return 0;
> -	return (so->so_rcv.sb_state & SS_CANTRCVMORE) || so->so_qlen ||
> +	return (so->so_rcv.sb_state & SS_CANTRCVMORE) ||
>  	    so->so_error || so->so_rcv.sb_cc >= so->so_rcv.sb_lowat;
>  }
>