From a7cce8b741b0870b12232bc993b6733b17df3e64 Mon Sep 17 00:00:00 2001
From: David du Colombier <0intro@gmail.com>
Date: Fri, 8 Jan 1999 00:00:00 +0000
Subject: [PATCH] Plan 9 from Bell Labs 1999-01-08

---
 port/devproc.c |  2 ++
 port/fault.c   | 47 ++++++++++++++++++++++++++++++++++-------------
 port/page.c    | 13 +++++++++++--
 port/portdat.h |  2 ++
 port/portfns.h |  1 +
 port/proc.c    |  2 ++
 port/swap.c    | 44 ++++++++++++++++++++++++++++++++++++--------
 port/sysproc.c | 22 ++++++++++++++++++++++
 8 files changed, 110 insertions(+), 23 deletions(-)

diff --git a/port/devproc.c b/port/devproc.c
index ef5ff1d58bc28d9ab77b8502bd2b039bf782a3f6..19a1c066bf6464ccb1ae8380188ee78dfa638e19 100644
--- a/port/devproc.c
+++ b/port/devproc.c
@@ -975,6 +975,7 @@ txt2data(Proc *p, Segment *s)
 	ps->flen = s->flen;
 	ps->flushme = 1;
 
+	qlock(&p->seglock);
 	for(i = 0; i < NSEG; i++)
 		if(p->seg[i] == s)
 			break;
@@ -985,6 +986,7 @@ txt2data(Proc *p, Segment *s)
 	putseg(s);
 	qlock(&ps->lk);
 	p->seg[i] = ps;
+	qunlock(&p->seglock);
 
 	return ps;
 }
diff --git a/port/fault.c b/port/fault.c
index 99d4dcb88ed1796895ce9a4a0790fe002dd03b38..1efa3894dba4e0de796954087216a0c2312b58cf 100644
--- a/port/fault.c
+++ b/port/fault.c
@@ -51,6 +51,7 @@ int
 fixfault(Segment *s, ulong addr, int read, int doputmmu)
 {
 	int type;
+	int ref;
 	Pte **p, *etp;
 	char buf[ERRLEN];
 	ulong va, mmuphys=0, soff;
@@ -92,6 +93,11 @@ fixfault(Segment *s, ulong addr, int read, int doputmmu)
 
 		lkp = *pg;
 		lock(lkp);
+
+		/* uncache the current page (since we may be changing it)
+		 * and, if a text page, put a duplicate back onto
+		 * the free list
+		 */
 		if(lkp->image)
 			duppage(lkp);
 		unlock(lkp);
@@ -129,7 +135,11 @@ fixfault(Segment *s, ulong addr, int read, int doputmmu)
 
 		lkp = *pg;
 		lock(lkp);
-		if(lkp->ref > 1) {
+		if(lkp->image == &swapimage && lkp->daddr)
+			ref = lkp->ref + swapcount(lkp->daddr);
+		else
+			ref = lkp->ref;
+		if(ref > 1) {
 			unlock(lkp);
 			new = newpage(0, &s, addr);
 			if(s == 0)
@@ -139,7 +149,8 @@ fixfault(Segment *s, ulong addr, int read, int doputmmu)
 			putpage(lkp);
 		}
 		else {
-			/* put a duplicate of a text page back onto
+			/* uncache the current page (since we may be changing it)
+			 * and, if a text page, put a duplicate back onto
 			 * the free list
 			 */
 			if(lkp->image)
@@ -181,7 +192,7 @@ fixfault(Segment *s, ulong addr, int read, int doputmmu)
 void
 pio(Segment *s, ulong addr, ulong soff, Page **p)
 {
-	Page *new;
+	Page *new, *new2;
 	KMap *k;
 	Chan *c;
 	int n, ask;
@@ -197,7 +208,7 @@ pio(Segment *s, ulong addr, ulong soff, Page **p)
 	else {
 		daddr = swapaddr(loadrec);
 		new = lookpage(&swapimage, daddr);
-		if(new)
+		if(new != nil)
 			putswap(loadrec);
 	}
 
@@ -235,7 +246,8 @@ pio(Segment *s, ulong addr, ulong soff, Page **p)
 		poperror();
 		kunmap(k);
 		qlock(&s->lk);
-		if(*p == 0) { 		/* Someone may have got there first */
+		/* race, we may have multiple simultaneous reads */
+		if(*p == 0) { 
 			new->daddr = daddr;
 			cachepage(new, s->image);
 			*p = new;
@@ -245,10 +257,21 @@ pio(Segment *s, ulong addr, ulong soff, Page **p)
 	}
 	else {				/* This is paged out */
 		c = swapimage.c;
+		qlock(&swapimage.rdlock);	/* mutex */
+
+		new2 = lookpage(&swapimage, daddr);
+		if(new2 != nil){
+			putpage(new);
+			putswap(*p);
+			*p = new2;
+			qunlock(&swapimage.rdlock);
+			return;
+		}
 
 		if(waserror()) {
 			kunmap(k);
 			putpage(new);
+			qunlock(&swapimage.rdlock);
 			qlock(&s->lk);
 			qunlock(&s->lk);
 			faulterror("sys: page in I/O error");
@@ -262,14 +285,12 @@ pio(Segment *s, ulong addr, ulong soff, Page **p)
 		kunmap(k);
 		qlock(&s->lk);
 
-		if(pagedout(*p)) {
-			new->daddr = daddr;
-			cachepage(new, &swapimage);
-			putswap(*p);
-			*p = new;
-		}
-		else
-			putpage(new);
+		new->daddr = daddr;
+		putswap(*p);
+		cachepage(new, &swapimage);
+		*p = new;
+
+		qunlock(&swapimage.rdlock);
 	}
 
 	if(s->flushme)
diff --git a/port/page.c b/port/page.c
index 847f70b64f3470cc7799491359c75559862ea5b0..f93a21dc6e4903edbfc1b3752dbe849b832ddafd 100644
--- a/port/page.c
+++ b/port/page.c
@@ -270,10 +270,16 @@ retry:
 	if(retries++ > 10000)
 		panic("duppage %d", retries);
 
-	/* No dup for swap/cache pages */
-	if(p->ref == 0 || p->image == nil || p->image->notext)
+	/* don't dup pages with no image */
+	if(p->ref == 0 || p->image == nil)
 		return;
 
+	/* No dup for swap/cache pages but we still have to uncache */
+	if(p->image->notext){
+		uncachepage(p);
+		return;
+	}
+
 	/*
 	 *  normal lock ordering is to call
 	 *  lock(&palloc) before lock(p).
@@ -390,6 +396,9 @@ cachedel(Image *i, ulong daddr)
 	for(f = *l; f; f = f->hash) {
 		if(f->image == i && f->daddr == daddr) {
 			*l = f->hash;
+			putimage(f->image);
+			f->image = 0;
+			f->daddr = 0;
 			break;
 		}
 		l = &f->hash;
diff --git a/port/portdat.h b/port/portdat.h
index bc56295b5f8ad21e0a06e863c26b964c8a5d21a2..a610d2db883a317e2cd623313c5fa152a91c1e12 100644
--- a/port/portdat.h
+++ b/port/portdat.h
@@ -326,6 +326,7 @@ struct Image
 	Image	*hash;			/* Qid hash chains */
 	Image	*next;			/* Free list */
 	int	notext;			/* no file associated */
+	QLock	rdlock;			/* mutex for reading from image */
 };
 
 struct Pte
@@ -543,6 +544,7 @@ struct Proc
 	int	state;
 	char	*psstate;	/* What /proc/#/status reports */
 	Segment	*seg[NSEG];
+	QLock	seglock;	/* locked whenever seg[] changes */
 	ulong	pid;
 	ulong	noteid;		/* Equivalent of note group */
 
diff --git a/port/portfns.h b/port/portfns.h
index ecaaf088f3234f9a177856f490590ee270c51b34..b5d9373cb7f0a3987acee5171b0522ae2100f34d 100644
--- a/port/portfns.h
+++ b/port/portfns.h
@@ -293,6 +293,7 @@ int		spllo(void);
 void		splx(int);
 void		splxpc(int);
 void		srvrecover(Chan*, Chan*);
+int		swapcount(ulong);
 void		swapinit(void);
 Block*		trimblock(Block*, int, int);
 void		tsleep(Rendez*, int (*)(void*), void*, int);
diff --git a/port/proc.c b/port/proc.c
index 5367e2a49547d7f18dee07c990229b2428c80cde..98399b6a66a0a480cf569f60f885e40ab98d4de8 100644
--- a/port/proc.c
+++ b/port/proc.c
@@ -796,6 +796,7 @@ pexit(char *exitstr, int freemem)
 	if(!freemem)
 		addbroken(up);
 
+	qlock(&up->seglock);
 	es = &up->seg[NSEG];
 	for(s = up->seg; s < es; s++) {
 		if(*s) {
@@ -803,6 +804,7 @@ pexit(char *exitstr, int freemem)
 			*s = 0;
 		}
 	}
+	qunlock(&up->seglock);
 
 	lock(&up->exl);		/* Prevent my children from leaving waits */
 	up->pid = 0;
diff --git a/port/swap.c b/port/swap.c
index a098d981955d3610a8f7b19525f21f583483750a..dd911d5ed241b9f100f73eb06f8b5bc70b761e71 100644
--- a/port/swap.c
+++ b/port/swap.c
@@ -60,6 +60,8 @@ putswap(Page *p)
 	lock(&swapalloc);
 	idx = &swapalloc.swmap[((ulong)p)/BY2PG];
 	if(--(*idx) == 0) {
+		if(swapalloc.swmap[((ulong)p)/BY2PG]==255)
+			panic("putswap");
 		swapalloc.free++;
 		if(idx < swapalloc.last)
 			swapalloc.last = idx;
@@ -71,10 +73,18 @@ void
 dupswap(Page *p)
 {
 	lock(&swapalloc);
+	if(swapalloc.swmap[((ulong)p)/BY2PG]==255)
+		panic("dupswap");
 	swapalloc.swmap[((ulong)p)/BY2PG]++;
 	unlock(&swapalloc);
 }
 
+int
+swapcount(ulong daddr)
+{
+	return swapalloc.swmap[daddr/BY2PG];
+}
+
 void
 kickpager(void)
 {
@@ -106,17 +116,21 @@ loop:
 	sleep(&swapalloc.r, needpages, 0);
 
 	while(needpages(junk)) {
-		p++;
-		if(p >= ep)
-			p = proctab(0);
-
-		if(p->state == Dead || p->kp)
-			continue;
 
 		if(swapimage.c) {
+			p++;
+			if(p >= ep)
+				p = proctab(0);
+	
+			if(p->state == Dead || p->kp)
+				continue;
+
+			qlock(&p->seglock);
 			for(i = 0; i < NSEG; i++) {
-				if(!needpages(junk))
+				if(!needpages(junk)){
+					qunlock(&p->seglock);
 					goto loop;
+				}
 
 				if(s = p->seg[i]) {
 					switch(s->type&SG_TYPE) {
@@ -141,6 +155,7 @@ loop:
 					}
 				}
 			}
+			qunlock(&p->seglock);
 		}
 		else {
 			if(!cpuserver)
@@ -264,12 +279,24 @@ pagepte(int type, Page **pg)
 	case SG_SHARED:
 	case SG_SHDATA:
 	case SG_MAP:
+		/* if it's already on disk, we're done */
+#ifdef asdf
+		lock(outp);
+		if(outp->daddr != 0 && outp->image == &swapimage){
+			dupswap((Page*)outp->daddr);
+			*pg = (Page*)(outp->daddr|PG_ONSWAP);
+			unlock(outp);
+			putpage(outp);
+			return;
+		}
+		unlock(outp);
+#endif asdf
+
 		daddr = newswap();
 		cachedel(&swapimage, daddr);
 		lock(outp);
 		outp->ref++;
 		uncachepage(outp);
-		unlock(outp);
 
 		/* Enter swap page into cache before segment is unlocked so that
 		 * a fault will cause a cache recovery rather than a pagein on a
@@ -278,6 +305,7 @@ pagepte(int type, Page **pg)
 		outp->daddr = daddr;
 		cachepage(outp, &swapimage);
 		*pg = (Page*)(daddr|PG_ONSWAP);
+		unlock(outp);
 
 		/* Add me to IO transaction list */
 		iolist[ioptr++] = outp;
diff --git a/port/sysproc.c b/port/sysproc.c
index 5e3a6d65ac570b9354b6bee2fe119c381ab9b7c7..0ebdf50cc9249b53fe221229ad44eea39beedc49 100644
--- a/port/sysproc.c
+++ b/port/sysproc.c
@@ -92,9 +92,16 @@ sysrfork(ulong *arg)
 
 	/* Make a new set of memory segments */
 	n = flag & RFMEM;
+	qlock(&p->seglock);
+	if(waserror()){
+		qunlock(&p->seglock);
+		nexterror();
+	}
 	for(i = 0; i < NSEG; i++)
 		if(up->seg[i])
 			p->seg[i] = dupseg(up->seg, i, n);
+	qunlock(&p->seglock);
+	poperror();
 
 	/* File descriptors */
 	if(flag & (RFFDG|RFCFDG)) {
@@ -304,6 +311,11 @@ sysexec(ulong *arg)
 	if(spage > TSTKSIZ)
 		error(Enovmem);
 
+	qlock(&up->seglock);
+	if(waserror()){
+		qunlock(&up->seglock);
+		nexterror();
+	}
 	up->seg[ESEG] = newseg(SG_STACK, TSTKTOP-USTKSIZE, USTKSIZE/BY2PG);
 
 	/*
@@ -383,6 +395,8 @@ sysexec(ulong *arg)
 	s = up->seg[ESEG];
 	up->seg[ESEG] = 0;
 	up->seg[SSEG] = s;
+	qunlock(&up->seglock);
+	poperror();
 	s->base = USTKTOP-USTKSIZE;
 	s->top = USTKTOP;
 	relocateseg(s, USTKTOP-TSTKTOP);
@@ -587,6 +601,12 @@ syssegdetach(ulong *arg)
 	ulong addr;
 	Segment *s;
 
+	qlock(&up->seglock);
+	if(waserror()){
+		qunlock(&up->seglock);
+		nexterror();
+	}
+
 	s = 0;
 	addr = arg[0];
 	for(i = 0; i < NSEG; i++)
@@ -609,6 +629,8 @@ found:
 	up->seg[i] = 0;
 	qunlock(&s->lk);
 	putseg(s);
+	qunlock(&up->seglock);
+	poperror();
 
 	/* Ensure we flush any entries from the lost segment */
 	flushmmu();