# HG changeset patch
# User yamahata@xxxxxxxxxxxxx
# Date 1162386794 -32400
# Node ID db676284c05accf621e6635cd2f93f890ecf25ae
# Parent  f9d0ee0d7de12861b809af224220e247a3ea9c66
[BLKTAP] avoid race between tapdisk and xvd daemon with ufe_ring.
- tapdisk updates rsp_cons by ioctl(). on the other hand xvd daemon reads
  rsp_cons in do_block_io_op() with RING_FULL().
  copy request and memory barrier before updating rsp_cons.
- tapdisk access req_prod_pvt with select(). on the other hand xvd daemon
  updates it in do_block_io_op().
- add NULL check to blktap_release()
PATCHNAME: blktap_mb_fix

Signed-off-by: Isaku Yamahata <yamahata@xxxxxxxxxxxxx>

diff -r f9d0ee0d7de1 -r db676284c05a linux-2.6-xen-sparse/drivers/xen/blktap/blktap.c
--- a/linux-2.6-xen-sparse/drivers/xen/blktap/blktap.c	Thu Nov 02 12:04:57 2006 +0900
+++ b/linux-2.6-xen-sparse/drivers/xen/blktap/blktap.c	Wed Nov 01 22:13:14 2006 +0900
@@ -538,8 +538,10 @@ static int blktap_release(struct inode *
 	}
 	
 	if ( (info->status != CLEANSHUTDOWN) && (info->blkif != NULL) ) {
-		kthread_stop(info->blkif->xenblkd);
-		info->blkif->xenblkd = NULL;
+		if (info->blkif->xenblkd != NULL) {
+			kthread_stop(info->blkif->xenblkd);
+			info->blkif->xenblkd = NULL;
+		}
 		info->status = CLEANSHUTDOWN;
 	}	
 	return 0;
@@ -1005,11 +1007,14 @@ static int blktap_read_ufe_ring(tap_blki
 	rmb();
         
 	for (i = info->ufe_ring.rsp_cons; i != rp; i++) {
+		blkif_response_t res;
 		resp = RING_GET_RESPONSE(&info->ufe_ring, i);
+		memcpy(&res, resp, sizeof(res));
+		mb();
 		++info->ufe_ring.rsp_cons;
 
 		/*retrieve [usr_idx] to [mmap_idx,pending_idx] mapping*/
-		usr_idx = (int)resp->id;
+		usr_idx = (int)res.id;
 		pending_idx = MASK_PEND_IDX(ID_TO_IDX(info->idx_map[usr_idx]));
 		mmap_idx = ID_TO_MIDX(info->idx_map[usr_idx]);
 
@@ -1042,8 +1047,8 @@ static int blktap_read_ufe_ring(tap_blki
 			map[offset] = NULL;
 		}
 		fast_flush_area(pending_req, pending_idx, usr_idx, info->minor);
-		make_response(blkif, pending_req->id, resp->operation,
-			      resp->status);
+		make_response(blkif, pending_req->id, res.operation,
+			      res.status);
 		info->idx_map[usr_idx] = INVALID_REQ;
 		blkif_put(pending_req->blkif);
 		free_req(pending_req);
@@ -1132,6 +1137,7 @@ static int do_block_io_op(blkif_t *blkif
 		}
 
 		memcpy(&req, RING_GET_REQUEST(blk_ring, rc), sizeof(req));
+		mb(); /* make_response() reads req_cons asynchronously */
 		blk_ring->req_cons = ++rc; /* before make_response() */	
 
 		switch (req.operation) {
@@ -1328,6 +1334,7 @@ static void dispatch_rw_block_io(blkif_t
 				  info->ufe_ring.req_prod_pvt);
 	memcpy(target, req, sizeof(*req));
 	target->id = usr_idx;
+	wmb(); /* blktap_poll() reads req_prod_pvt asynchronously */
 	info->ufe_ring.req_prod_pvt++;
 	return;