Re: schedcpu() in /sys/kern/sched_4bsd.c calls thread_lock() on thread with un-initialized td_lock

On Thursday, March 31, 2011 12:21:45 pm Svatopluk Kraus wrote:
> On Thu, Mar 31, 2011 at 3:58 PM, John Baldwin <jhb_at_freebsd.org> wrote:
> > On Thursday, March 31, 2011 7:32:26 am Svatopluk Kraus wrote:
> >> Hi,
> >>
> >>   I've got a page fault (because of NULL td_lock) in
> >> thread_lock_flags() called from schedcpu() in /sys/kern/sched_4bsd.c
> >> file. During process fork, new thread is linked to new process which
> >> is linked to allproc list and both allproc_lock and new process lock
> >> are unlocked before sched_fork() is called, where new thread td_lock
> >> is initialized. Only PRS_NEW process status is on sentry but not
> >> checked in schedcpu().
> >
> > I think this should fix it:
> >
> > Index: sched_4bsd.c
> > ===================================================================
> > --- sched_4bsd.c        (revision 220190)
> > +++ sched_4bsd.c        (working copy)
> > _at__at_ -463,6 +463,10 _at__at_ schedcpu(void)
> >        sx_slock(&allproc_lock);
> >        FOREACH_PROC_IN_SYSTEM(p) {
> >                PROC_LOCK(p);
> > +               if (p->p_state == PRS_NEW) {
> > +                       PROC_UNLOCK(p);
> > +                       continue;
> > +               }
> >                FOREACH_THREAD_IN_PROC(p, td) {
> >                        awake = 0;
> >                        thread_lock(td);
> >
> 
> Thanks for patch. Maybe, test p_state not to be PRS_NORMAL could be better?

I thought about that, but zombies are always moved to zombproc atomically
with changing p_state (and under an exclusive allproc_lock) and all the
other places currently use this type of check.

> I've got next (same reason) page fault in thread_lock_flags() called
> from scheduler() in sys/vm/vm_glue.c. I try to search for
> FOREACH_THREAD_IN_PROC() together with FOREACH_PROC_IN_SYSTEM() in
> /sys subtree and next problem could be in deadlkres() in
> sys/kern/kern_clock.c at least.

Here is a larger patch:

Index: kern/kern_ktrace.c
===================================================================
--- kern/kern_ktrace.c	(revision 220190)
+++ kern/kern_ktrace.c	(working copy)
_at__at_ -882,7 +882,8 _at__at_
 		nfound = 0;
 		LIST_FOREACH(p, &pg->pg_members, p_pglist) {
 			PROC_LOCK(p);
-			if (p_cansee(td, p) != 0) {
+			if (p->p_state == PRS_NEW ||
+			    p_cansee(td, p) != 0) {
 				PROC_UNLOCK(p); 
 				continue;
 			}
Index: kern/kern_sig.c
===================================================================
--- kern/kern_sig.c	(revision 220190)
+++ kern/kern_sig.c	(working copy)
_at__at_ -1799,7 +1799,8 _at__at_
 		PGRP_LOCK_ASSERT(pgrp, MA_OWNED);
 		LIST_FOREACH(p, &pgrp->pg_members, p_pglist) {
 			PROC_LOCK(p);
-			if (checkctty == 0 || p->p_flag & P_CONTROLT)
+			if (p->p_state == PRS_NORMAL &&
+			    (checkctty == 0 || p->p_flag & P_CONTROLT))
 				pksignal(p, sig, ksi);
 			PROC_UNLOCK(p);
 		}
_at__at_ -3313,7 +3314,8 _at__at_
 		PGRP_LOCK(sigio->sio_pgrp);
 		LIST_FOREACH(p, &sigio->sio_pgrp->pg_members, p_pglist) {
 			PROC_LOCK(p);
-			if (CANSIGIO(sigio->sio_ucred, p->p_ucred) &&
+			if (p->p_state == PRS_NORMAL &&
+			    CANSIGIO(sigio->sio_ucred, p->p_ucred) &&
 			    (checkctty == 0 || (p->p_flag & P_CONTROLT)))
 				psignal(p, sig);
 			PROC_UNLOCK(p);
Index: kern/kern_clock.c
===================================================================
--- kern/kern_clock.c	(revision 220190)
+++ kern/kern_clock.c	(working copy)
_at__at_ -201,6 +201,10 _at__at_
 		tryl = 0;
 		FOREACH_PROC_IN_SYSTEM(p) {
 			PROC_LOCK(p);
+			if (p->p_state == PRS_NEW) {
+				PROC_UNLOCK(p);
+				continue;
+			}
 			FOREACH_THREAD_IN_PROC(p, td) {
 
 				/*
Index: kern/sched_4bsd.c
===================================================================
--- kern/sched_4bsd.c	(revision 220190)
+++ kern/sched_4bsd.c	(working copy)
_at__at_ -463,6 +463,10 _at__at_
 	sx_slock(&allproc_lock);
 	FOREACH_PROC_IN_SYSTEM(p) {
 		PROC_LOCK(p);
+		if (p->p_state == PRS_NEW) {
+			PROC_UNLOCK(p);
+			continue;
+		}
 		FOREACH_THREAD_IN_PROC(p, td) {
 			awake = 0;
 			thread_lock(td);
Index: kern/kern_resource.c
===================================================================
--- kern/kern_resource.c	(revision 220190)
+++ kern/kern_resource.c	(working copy)
_at__at_ -129,7 +129,8 _at__at_
 		sx_sunlock(&proctree_lock);
 		LIST_FOREACH(p, &pg->pg_members, p_pglist) {
 			PROC_LOCK(p);
-			if (p_cansee(td, p) == 0) {
+			if (p->p_state == PRS_NORMAL &&
+			    p_cansee(td, p) == 0) {
 				if (p->p_nice < low)
 					low = p->p_nice;
 			}
_at__at_ -215,7 +216,8 _at__at_
 		sx_sunlock(&proctree_lock);
 		LIST_FOREACH(p, &pg->pg_members, p_pglist) {
 			PROC_LOCK(p);
-			if (p_cansee(td, p) == 0) {
+			if (p->p_state == PRS_NORMAL &&
+			    p_cansee(td, p) == 0) {
 				error = donice(td, p, uap->prio);
 				found++;
 			}
_at__at_ -230,7 +232,8 _at__at_
 		sx_slock(&allproc_lock);
 		FOREACH_PROC_IN_SYSTEM(p) {
 			PROC_LOCK(p);
-			if (p->p_ucred->cr_uid == uap->who &&
+			if (p->p_state == PRS_NORMAL &&
+			    p->p_ucred->cr_uid == uap->who &&
 			    p_cansee(td, p) == 0) {
 				error = donice(td, p, uap->prio);
 				found++;
Index: vm/vm_glue.c
===================================================================
--- vm/vm_glue.c	(revision 220190)
+++ vm/vm_glue.c	(working copy)
_at__at_ -730,7 +730,8 _at__at_
 	sx_slock(&allproc_lock);
 	FOREACH_PROC_IN_SYSTEM(p) {
 		PROC_LOCK(p);
-		if (p->p_flag & (P_SWAPPINGOUT | P_SWAPPINGIN | P_INMEM)) {
+		if (p->p_state == PRS_NEW ||
+		    p->p_flag & (P_SWAPPINGOUT | P_SWAPPINGIN | P_INMEM)) {
 			PROC_UNLOCK(p);
 			continue;
 		}

-- 
John Baldwin