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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
This commit is contained in:
cl 2003-10-31 23:36:50 +00:00
parent 8904362ede
commit 8edffb7356
1 changed files with 9 additions and 15 deletions
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24
sys/kern/kern_sa.c
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@ -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 @@ sa_upcall_userret(struct lwp *l)
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 @@ sa_upcall_userret(struct lwp *l)
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 @@ sa_vp_repossess(struct lwp *l)
* 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 @@ sa_vp_repossess(struct lwp *l)
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 @@ sa_vp_donate(struct lwp *l)
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;