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, 8 insertions, 0 deletions

diff --git a/sys/kern/kern_ktrace.c b/sys/kern/kern_ktrace.c
index db44873..6fc46d6 100644
--- a/sys/kern/kern_ktrace.c
+++ b/sys/kern/kern_ktrace.c
@@ -350,16 +350,24 @@ ktrace(td, uap)
 		/*
 		 * by process group
 		 */
+		PGRPSESS_SLOCK();
 		pg = pgfind(-uap->pid);
 		if (pg == NULL) {
+			PGRPSESS_SUNLOCK();
 			error = ESRCH;
 			goto done;
 		}
+		/*
+		 * ktrops() may call vrele(). Lock pg_members
+		 * by the pgrpsess_lock rather than pg_mtx.
+		 */
+		PGRP_UNLOCK(pg);
 		LIST_FOREACH(p, &pg->pg_members, p_pglist)
 			if (descend)
 				ret |= ktrsetchildren(curp, p, ops, facs, vp);
 			else
 				ret |= ktrops(curp, p, ops, facs, vp);
+		PGRPSESS_SUNLOCK();
 	} else {
 		/*
 		 * by pid