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gefs: fix fidtab locking order in clunkfid()

Do not abuse fidtab lock for serializing
clunking.

The clunk should serialize on Fid.Lock
instead, so add a canlock check here.

The lock order is strictly:

Fid.Lock > Conn.fidtab[x].Lock

--- a/sys/src/cmd/gefs/fs.c

+++ b/sys/src/cmd/gefs/fs.c

@@ -769,6 +769,11 @@

 	return n;

 }

+/*

+ * clunkfid() removes a fid from the

+ * connection fid tab and drops reference.

+ * Fid must be locked.

+ */

 static void

 clunkfid(Conn *c, Fid *fid, Amsg **ao)

 {

@@ -775,6 +780,8 @@

 	Fid *f, **pf;

 	u32int h;

+	assert(!canlock(fid));

+

 	h = ihash(fid->fid) % Nfidtab;

 	lock(&c->fidtablk[h]);

 	pf = &c->fidtab[h];

@@ -786,6 +793,8 @@

 		}

 		pf = &f->next;

 	}

+	unlock(&c->fidtablk[h]);

+

 	assert(f != nil);

 	if(f->scan != nil){

 		free(f->scan);

@@ -811,7 +820,6 @@

 		(*ao)->end = f->dent->length;

 		(*ao)->dent = f->dent;

 	}

-	unlock(&c->fidtablk[h]);

 }

 static int

@@ -1796,8 +1804,8 @@

 	}

 	t = f->mnt->root;

 	nm = 0;

-	*ao = nil;

 	lock(f);

+	*ao = nil;

 	clunkfid(m->conn, f, ao);

 	/* rclose files are getting removed here anyways */

 	if(*ao != nil)

@@ -2291,7 +2299,7 @@

 {

 	Conn **pp;

 	Amsg *a;

-	Fid *f, *nf;

+	Fid *f;

 	int i;

 	if(adec(&c->ref) != 0)

@@ -2313,19 +2321,25 @@

 		close(c->cfd);

 	for(i = 0; i < Nfidtab; i++){

-		lock(&c->fidtablk[i]);

-		for(f = c->fidtab[i]; f != nil; f = nf){

-			nf = f->next;

+		for(;;){

+			lock(&c->fidtablk[i]);

+			f = c->fidtab[i];

+			if(f == nil){

+				unlock(&c->fidtablk[i]);

+				break;

+			}

 			ainc(&f->ref);

+			unlock(&c->fidtablk[i]);

+			

 			lock(f);

 			a = nil;

 			clunkfid(c, f, &a);

 			unlock(f);

 			putfid(f);

+

 			if(a != nil)

 				chsend(fs->admchan, a);

 		}

-		unlock(&c->fidtablk[i]);

 	}

 	free(c);

 }

-- 

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