code: mafs

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attempt to fix the deadlock between putwrite() and dowrite()

--- a/9p.c

+++ b/9p.c

@@ -1303,7 +1303,6 @@

 		if(buf == nil)

 			return -1;

-

 		howmuch = min(Blocksize-lastblksize, wbufsize);

 		if(chatty9p > 1)

 		dprint("fill lastblksize %llud howmuch %llud\n",

--- a/all.h

+++ b/all.h

@@ -76,7 +76,7 @@

 		u8	*xiobuf;	/* "real" buffer pointer */

 		Content *io;	/* cast'able to contents */

 	};

-	u32	dirties;	/* number of dirty blocks yet to be written by the writer */

+	u64	dirties;	/* number of dirty blocks yet to be written by the writer */

 	u8 tofree;		/* free this Iobuf after the dirty blocks are written to the disk */

 };

--- a/writer.c

+++ b/writer.c

@@ -92,13 +92,14 @@

 		have wlock()'ed the Iobuf too */

 	if(drts.head != nil){

 		b = pluck(drts.head);

-		rwakeup(&drts.isfull);

+		if(drts.n == npendingwrites-1)

+			rwakeup(&drts.isfull);

+		if(chatty9p > 4 && b!=nil){

+			dprint("getwrite done b->blkno %llud\n", b->blkno);

+		stats();

+		}

 	}else

 		b = nil;

-	if(chatty9p > 4 && b!=nil){

-		dprint("getwrite done b->blkno %llud\n", b->blkno);

-		stats();

-	}

 	qunlock(&drts.lck);

 	return b;

 }

@@ -109,17 +110,31 @@

 {

 	Wbuf *w;

+	/*

+		copying contents to w before.

+		This avoids rsleep'ing while holding a wlock() on the Iobuf.

+		rsleep'ing while holding the wlock() causes a deadlock()

+		with dowrite() when it tries to decrement dirties by holding

+		a wlock() on the Iobuf.

+	*/

+	w = emalloc9p(sizeof(Wbuf));

+	w->blkno = b->blkno;

+	w->payload = allocmemunit();

+	memcpy(w->payload, b->xiobuf, Rawblocksize);

+	b->dirties++;

+	w->iobuf = b;

+	if(chkwunlock(b) == 0){

+		showbuf(b);

+		panic("putwrite chkwunlock(p) == 0 called by %#p\n", getcallerpc(&b));

+	}

+

 	qlock(&drts.lck);

 	if(chatty9p > 4){

 		dprint("putwrite start p->blkno %llud\n", b->blkno);

 		stats();

 	}

-	if(drts.n > npendingwrites)

+	if(drts.n == npendingwrites)

 		rsleep(&drts.isfull);

-	w = emalloc9p(sizeof(Wbuf));

-	w->blkno = b->blkno;

-	w->payload = allocmemunit();

-	memcpy(w->payload, b->xiobuf, Rawblocksize);

 	if(drts.head == nil){

 		drts.head = drts.tail = w;

 	}else{

@@ -130,12 +145,6 @@

 	drts.n++;

 	if(drts.n == 1)

 		rwakeup(&drts.isempty);

-	b->dirties++;

-	w->iobuf = b;

-	if(chkwunlock(b) == 0){

-		showbuf(b);

-		panic("putwrite chkwunlock(p) == 0 called by %#p\n", getcallerpc(&b));

-	}

 	if(chatty9p > 4 && b!=nil){

 		dprint("putwrite done b->blkno %llud\n", b->blkno);

 		stats();