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fs; make mounts participate in deferred reclamation

there was a deadlock with the mountlk, where both sides
of the channel required the mountlk to be held; this could
be fixed in several ways, but the most elegant is eliminating
the lock entirely. The data isn't mutated often.

--- a/dat.h

+++ b/dat.h

@@ -434,6 +434,7 @@

 enum {

 	DFblk,

+	DFmnt,

 	DFtree,

 };

@@ -440,6 +441,7 @@

 struct Bfree {

 	Bfree	*next;

 	int	op;

+	Mount	*m;

 	Tree	*t;

 	Blk	*b;

 	Bptr	bp;

@@ -507,7 +509,6 @@

 	QLock	synclk;

 	Rendez	syncrz;

-	Lock	mountlk;

 	Mount	*mounts;

 	Mount	*snapmnt;

 	Lock	connlk;

--- a/fs.c

+++ b/fs.c

@@ -86,11 +86,9 @@

 	 *  can take a consistent snapshot.

          */

 	qlock(&fs->mutlk);

-	lock(&fs->mountlk);

 	dlsync();

-	for(mnt = fs->mounts; mnt != nil; mnt = mnt->next)

+	for(mnt = agetp(&fs->mounts); mnt != nil; mnt = mnt->next)

 		updatesnap(&mnt->root, mnt->root, mnt->name);

-	unlock(&fs->mountlk);

 	for(i = 0; i < fs->narena; i++){

 		a = &fs->arenas[i];

 		qlock(a);

@@ -174,15 +172,13 @@

 	Tree *t, *s;

 	Mount *mnt;

-	lock(&fs->mountlk);

 	if(waserror()){

 		*tp = nil;

-		unlock(&fs->mountlk);

 		nexterror();

 	}

 	t = nil;

 	*tp = nil;

-	for(mnt = fs->mounts; mnt != nil; mnt = mnt->next){

+	for(mnt = agetp(&fs->mounts); mnt != nil; mnt = mnt->next){

 		if(strcmp(a->old, mnt->name) == 0){

 			updatesnap(&mnt->root, mnt->root, mnt->name);

 			t = agetp(&mnt->root);

@@ -193,7 +189,6 @@

 	if(t == nil && (t = opensnap(a->old, nil)) == nil){

 		if(a->fd != -1)

 			fprint(a->fd, "snap: open '%s': does not exist\n", a->old);

-		unlock(&fs->mountlk);

 		poperror();

 		return;

 	}

@@ -201,7 +196,6 @@

 		if(mnt != nil) {

 			if(a->fd != -1)

 				fprint(a->fd, "snap: snap is mounted: '%s'\n", a->old);

-			unlock(&fs->mountlk);

 			poperror();

 			return;

 		}

@@ -215,7 +209,6 @@

 			if(a->fd != -1)

 				fprint(a->fd, "snap: already exists '%s'\n", a->new);

 			closesnap(s);

-			unlock(&fs->mountlk);

 			poperror();

 			return;

 		}

@@ -222,7 +215,6 @@

 		tagsnap(t, a->new, a->flag);

 	}

 	closesnap(t);

-	unlock(&fs->mountlk);

 	poperror();

 	if(a->fd != -1){

 		if(a->delete)

@@ -593,8 +585,7 @@

 		return fs->snapmnt;

 	}

-	lock(&fs->mountlk);

-	for(mnt = fs->mounts; mnt != nil; mnt = mnt->next){

+	for(mnt = agetp(&fs->mounts); mnt != nil; mnt = mnt->next){

 		if(strcmp(name, mnt->name) == 0){

 			ainc(&mnt->ref);

 			goto Out;

@@ -604,7 +595,6 @@

 	if((mnt = mallocz(sizeof(*mnt), 1)) == nil)

 		error(Enomem);

 	if(waserror()){

-		unlock(&fs->mountlk);

 		free(mnt);

 		nexterror();

 	}

@@ -617,11 +607,10 @@

 	mnt->noauto = (flg & Lnoauto) != 0;

 	mnt->root = t;

 	mnt->next = fs->mounts;

-	fs->mounts = mnt;

+	asetp(&fs->mounts, mnt);

 	poperror();

 Out:

-	unlock(&fs->mountlk);

 	return mnt;

 }

@@ -629,10 +618,10 @@

 clunkmount(Mount *mnt)

 {

 	Mount *me, **p;

+	Bfree *f;

 	if(mnt == nil)

 		return;

-	lock(&fs->mountlk);

 	if(adec(&mnt->ref) == 0){

 		for(p = &fs->mounts; (me = *p) != nil; p = &me->next){

 			if(me == mnt)

@@ -639,10 +628,12 @@

 				break;

 		}

 		assert(me != nil);

+		f = emalloc(sizeof(Bfree), 0);

+		f->op = DFblk;

+		f->m = mnt;

 		*p = me->next;

-		free(mnt);

+		limbo(f);

 	}

-	unlock(&fs->mountlk);

 }

 static void

@@ -2509,8 +2500,7 @@

 		chsend(fs->admchan, a);

 		tmnow(&now, nil);

-		lock(&fs->mountlk);

-		for(mnt = fs->mounts; mnt != nil; mnt = mnt->next){

+		for(mnt = agetp(&fs->mounts); mnt != nil; mnt = mnt->next){

 			if(mnt->noauto)

 				continue;

 			if(now.yday != then.yday){

@@ -2533,7 +2523,6 @@

 				snapmsg("main", mnt->minutely[m], Lauto);

 			}

 		}

-		unlock(&fs->mountlk);

 		if(now.hour != then.hour)

 			h = (h+1)%24;

 		if(now.min != then.min)

--- a/snap.c

+++ b/snap.c

@@ -3,9 +3,9 @@

 #include <fcall.h>

 #include <avl.h>

+#include "atomic.h"

 #include "dat.h"

 #include "fns.h"

-#include "atomic.h"

 static void

 dlflush(Dlist *dl)

@@ -310,7 +310,7 @@

 	btupsert(&fs->snap, m, nm);

 	reclaimblocks(t->gen, succ, t->pred);

 	if(deltree){

-		for(mnt = fs->mounts; mnt != nil; mnt = mnt->next){

+		for(mnt = agetp(&fs->mounts); mnt != nil; mnt = mnt->next){

 			if(mnt->root->gen == t->succ)

 				mnt->root->pred = t->pred;

 			if(mnt->root->gen == t->pred)