shithub: gefs

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fs: fix some races

When enqueing a block, we could reorder the writes
when sorting by sync generation rather than quiesce
generation, which would lead to corrupt blocks.

When clunking a dent, we could end up decrementing
and not finding the entry in the table.

--- a/blk.c

+++ b/blk.c

@@ -650,6 +650,7 @@

 	b->bp.addr = bp;

 	b->bp.hash = -1;

 	b->bp.gen = fs->nextgen;

+	b->qgen = fs->qgen;

 	b->data = b->buf + Hdrsz;

 	b->fnext = nil;

@@ -875,6 +876,7 @@

 	if(!allquiesced)

 		return;

+	inc64(&fs->qgen, 1);

 	lock(&fs->freelk);

 	p = nil;

 	if(fs->freep != nil){

@@ -895,8 +897,8 @@

 int

 blkcmp(Blk *a, Blk *b)

 {

-	if(a->bp.gen != b->bp.gen)

-		return (a->bp.gen < b->bp.gen) ? -1 : 1;

+	if(a->qgen != b->qgen)

+		return (a->qgen < b->qgen) ? -1 : 1;

 	if(a->bp.addr != b->bp.addr)

 		return (a->bp.addr < b->bp.addr) ? -1 : 1;

 	return 0;

--- a/dat.h

+++ b/dat.h

@@ -450,7 +450,7 @@

 	Chan	*wrchan;

 	Chan	*rdchan;

 	int	nquiesce;

-

+	vlong	qgen;

 	Lock	activelk;

 	int	active[32];

 	int	lastactive[32];

@@ -621,7 +621,7 @@

 	Blk	*fnext;

 	long	flag;

-	long	syncgen;

+	long	qgen;

 	/* serialized to disk in header */

 	short	type;	/* @0, for all */

--- a/fs.c

+++ b/fs.c

@@ -369,21 +369,21 @@

 	Dent *e, **pe;

 	u32int h;

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

-		h = ihash(de->qid.path) % Ndtab;

-		lock(&fs->dtablk);

-		pe = &fs->dtab[h];

-		for(e = fs->dtab[h]; e != nil; e = e->next){

-			if(e == de){

-				*pe = e->next;

-				unlock(&fs->dtablk);

-				free(de);

-				return;

-			}

-			pe = &e->next;

-		}

-		abort();

+	lock(&fs->dtablk);

+	if(adec(&de->ref) != 0)

+		goto Out;

+	h = ihash(de->qid.path) % Ndtab;

+	pe = &fs->dtab[h];

+	for(e = fs->dtab[h]; e != nil; e = e->next){

+		if(e == de)

+			break;

+		pe = &e->next;

 	}

+	assert(e != nil);

+	*pe = e->next;

+	free(de);

+Out:

+	unlock(&fs->dtablk);

 }

 void