Lock struct pgrp, session and sigio.

New locks are:

- pgrpsess_lock which locks the whole pgrps and sessions,
- pg_mtx which protects the pgrp members, and
- s_mtx which protects the session members.

Please refer to sys/proc.h for the coverage of these locks.

Changes on the pgrp/session interface:

- pgfind() needs the pgrpsess_lock held.

- The caller of enterpgrp() is responsible to allocate a new pgrp and
  session.

- Call enterthispgrp() in order to enter an existing pgrp.

- pgsignal() requires a pgrp lock held.

Reviewed by:	jhb, alfred
Tested on:	cvsup.jp.FreeBSD.org
		(which is a quad-CPU machine running -current)

1 files changed, 15 insertions, 6 deletions

diff --git a/sys/kern/vfs_vnops.c b/sys/kern/vfs_vnops.c
index aba87d4..ab3e3c9 100644
--- a/sys/kern/vfs_vnops.c
+++ b/sys/kern/vfs_vnops.c
@@ -619,6 +619,7 @@ vn_ioctl(fp, com, data, td)
 	struct thread *td;
 {
 	register struct vnode *vp = ((struct vnode *)fp->f_data);
+	struct vnode *vpold;
 	struct vattr vattr;
 	int error;
 
@@ -656,15 +657,23 @@ vn_ioctl(fp, com, data, td)
 		if (error == 0 && com == TIOCSCTTY) {
 
 			/* Do nothing if reassigning same control tty */
-			if (td->td_proc->p_session->s_ttyvp == vp)
+			PGRPSESS_XLOCK();
+			if (td->td_proc->p_session->s_ttyvp == vp) {
+				PGRPSESS_XUNLOCK();
 				return (0);
+			}
 
-			/* Get rid of reference to old control tty */
-			if (td->td_proc->p_session->s_ttyvp)
-				vrele(td->td_proc->p_session->s_ttyvp);
-
-			td->td_proc->p_session->s_ttyvp = vp;
+			vpold = td->td_proc->p_session->s_ttyvp;
 			VREF(vp);
+			SESS_LOCK(td->td_proc->p_session);
+			td->td_proc->p_session->s_ttyvp = vp;
+			SESS_UNLOCK(td->td_proc->p_session);
+
+			PGRPSESS_XUNLOCK();
+
+			/* Get rid of reference to old control tty */
+			if (vpold)
+				vrele(vpold);
 		}
 		return (error);
 	}