Re: kern/60729: incosistent st_ino from the first stat(2) on a socket

["Taylor R Campbell via gnats" <gnats-admin%NetBSD.org@localhost>]

The following reply was made to PR kern/60729; it has been noted by GNATS.

From: Taylor R Campbell <riastradh%NetBSD.org@localhost>
To: uwe%NetBSD.org@localhost
Cc: gnats-bugs%NetBSD.org@localhost, netbsd-bugs%NetBSD.org@localhost
Subject: Re: kern/60729: incosistent st_ino from the first stat(2) on a socket
Date: Tue, 15 Sep 2026 16:49:49 +0000

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 # HG changeset patch
 # User Taylor R Campbell <riastradh%NetBSD.org@localhost>
 # Date 1789490537 0
 #      Tue Sep 15 16:42:17 2026 +0000
 # Branch trunk
 # Node ID 3fe1ba99ddf50e054ee728621b78ed85d138cc5d
 # Parent  4fbd288ac1da9e7d9592ddecf04f7513e244152f
 # EXP-Topic riastradh-pr60729-unixsockino
 uipc_usrreq: Fix unix-domain socket inode assignment.
 
 1. `if (unp->unp_ino =3D=3D 0) unp->unp_ino =3D unp_ino++' would assign
    zero the first time around by mistake, and then assign nonzero
    after that.  `if (unp->unp_ino =3D=3D 0) unp->unp_ino =3D ++unp_ino'
    avoids this silliness.
 
 2. Make the ++unp_ino part atomic.
 
 PR kern/60729: incosistent st_ino from the first stat(2) on a socket
 
 diff -r 4fbd288ac1da -r 3fe1ba99ddf5 sys/kern/uipc_usrreq.c
 --- a/sys/kern/uipc_usrreq.c	Mon Aug 10 13:36:10 2026 +0000
 +++ b/sys/kern/uipc_usrreq.c	Tue Sep 15 16:42:17 2026 +0000
 @@ -179,7 +179,16 @@ const struct sockaddr_un sun_noname =3D {
  	.sun_len =3D offsetof(struct sockaddr_un, sun_path),
  	.sun_family =3D AF_LOCAL,
  };
 -ino_t	unp_ino;			/* prototype for fake inode numbers */
 +
 +/* prototype for fake inode numbers */
 +#ifdef __HAVE_ATOMIC64_OPS
 +volatile uint64_t	unp_ino __cacheline_aligned;
 +#else
 +struct {
 +	uint64_t	num;
 +	kmutex_t	lock;
 +} unp_ino __cacheline_aligned;
 +#endif
 =20
  static struct mbuf * unp_addsockcred(struct lwp *, struct mbuf *);
  static void   unp_discard_later(file_t *);
 @@ -233,6 +242,10 @@ uipc_init(void)
  	    NULL, &unp_thread_lwp, "unpgc");
  	if (error !=3D 0)
  		panic("uipc_init %d", error);
 +
 +#ifndef __HAVE_ATOMIC64_OPS
 +	mutex_init(&unp_ino.lock, MUTEX_DEFAULT, IPL_NONE);
 +#endif
  }
 =20
  static void
 @@ -906,8 +919,15 @@ unp_stat(struct socket *so, struct stat=20
  		break;
  	}
  	ub->st_dev =3D NODEV;
 -	if (unp->unp_ino =3D=3D 0)
 -		unp->unp_ino =3D unp_ino++;
 +	if (unp->unp_ino =3D=3D 0) {
 +#ifdef __HAVE_ATOMIC64_OPS
 +		unp->unp_ino =3D atomic_inc_64_nv(&unp_ino);
 +#else
 +		mutex_enter(&unp_ino.lock);
 +		unp->unp_ino =3D ++unp_ino.num;
 +		mutex_exit(&unp_ino.lock);
 +#endif
 +	}
  	ub->st_atimespec =3D ub->st_mtimespec =3D ub->st_ctimespec =3D unp->unp_c=
 time;
  	ub->st_ino =3D unp->unp_ino;
  	ub->st_uid =3D so->so_uidinfo->ui_uid;
 
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