[src/trunk]: src/sys/kern Avoid race condition where an LWP is put into the c...

[cl <cl%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/bbf88e8af1e7
branches:  trunk
changeset: 554692:bbf88e8af1e7
user:      cl <cl%NetBSD.org@localhost>
date:      Fri Oct 31 23:36:50 2003 +0000

description:
Avoid race condition where an LWP is put into the cache before
its state is saved:
- don't sa_putcachelwp() in sa_vp_repossess/sa_vp_donate
- only defer saving the event LWP's state
- sa_putcachelwp() after the interrupted LWP's state is saved

diffstat:

 sys/kern/kern_sa.c |  24 +++++++++---------------
 1 files changed, 9 insertions(+), 15 deletions(-)

diffs (73 lines):

diff -r a08242788096 -r bbf88e8af1e7 sys/kern/kern_sa.c
--- a/sys/kern/kern_sa.c        Fri Oct 31 22:47:44 2003 +0000
+++ b/sys/kern/kern_sa.c        Fri Oct 31 23:36:50 2003 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: kern_sa.c,v 1.32 2003/10/31 22:47:44 cl Exp $  */
+/*     $NetBSD: kern_sa.c,v 1.33 2003/10/31 23:36:50 cl Exp $  */
 
 /*-
  * Copyright (c) 2001 The NetBSD Foundation, Inc.
@@ -37,7 +37,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_sa.c,v 1.32 2003/10/31 22:47:44 cl Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_sa.c,v 1.33 2003/10/31 23:36:50 cl Exp $");
 
 #include <sys/param.h>
 #include <sys/systm.h>
@@ -1154,8 +1154,8 @@
 
                DPRINTFN(9,("sa_upcall_userret(%d.%d) nstacks--   = %2d\n",
                    l->l_proc->p_pid, l->l_lid, sa->sa_nstacks));
-               if (sa_upcall0(l, SA_UPCALL_UNBLOCKED | SA_UPCALL_DEFER, l, l2, 0, NULL, sau,
-                   &st) != 0) {
+               if (sa_upcall0(l, SA_UPCALL_UNBLOCKED | SA_UPCALL_DEFER_EVENT,
+                       l, l2, 0, NULL, sau, &st) != 0) {
                        /*
                         * We were supposed to deliver an UNBLOCKED
                         * upcall, but don't have resources to do so.
@@ -1170,6 +1170,9 @@
                SIMPLEQ_INSERT_TAIL(&sa->sa_upcalls, sau, sau_next);
                l->l_flag |= L_SA_UPCALL;
                l->l_flag &= ~L_SA_BLOCKING;
+               SCHED_LOCK(s);
+               sa_putcachelwp(p, l2); /* PHOLD from sa_vp_repossess */
+               SCHED_UNLOCK(s);
 
                /* We migth have sneaked past signal handling and userret */
                SA_LWP_STATE_UNLOCK(l, f);
@@ -1346,10 +1349,6 @@
         * Put ourselves on the virtual processor and note that the
         * previous occupant of that position was interrupted.
         */
-
-
-
-
        l2 = sa->sa_vp;
        sa->sa_vp = l;
        if (sa->sa_idle == l2)
@@ -1375,12 +1374,7 @@
                            l2->l_stat);
 #endif
                }
-               sa_putcachelwp(p, l2);
-               /*
-                * XXX SMP race! Need to be sure that l2's state is
-                * captured before the upcall before we make it possible
-                * for another processor to grab it.
-                */
+               l2->l_stat = LSSUSPENDED;
                SCHED_UNLOCK(s);
        }
        return l2;
@@ -1457,7 +1451,7 @@
                        SCHED_LOCK(s);
                        
                        p->p_nrlwps--;
-                       sa_putcachelwp(p, l);
+                       l->l_stat = LSSUSPENDED;
                        sa->sa_vp = l2;
                        sa->sa_vp_wait_count--;
                        l2->l_flag &= ~L_SA_WANTS_VP;