[Patch-for-4.4] xen/blkback: don't use xen_blkif_get() in xen-blkback kthread

[Juergen Gross <jgross@suse.com>]

There is no need to use xen_blkif_get()/xen_blkif_put() in the kthread
of xen-blkback. Thread stopping is synchronous and using the blkif
reference counting in the kthread will avoid to ever let the reference
count drop to zero at the end of an I/O running concurrent to
disconnecting.

Setting ring->xenblkd to NULL after stopping the kthread isn't needed
as the kthread does this already.

Signed-off-by: Juergen Gross <jgross@suse.com>
Tested-by: Steven Haigh <netwiz@crc.id.au>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
---
This is a backport of commit a24fa22ce22ae302b3bf8f7008896d52d5d57b8d
for linux-4.4.y branch.
---
 drivers/block/xen-blkback/blkback.c | 3 ---
 drivers/block/xen-blkback/xenbus.c  | 1 -
 2 files changed, 4 deletions(-)

diff --git a/drivers/block/xen-blkback/blkback.c b/drivers/block/xen-blkback/blkback.c
index 41fb1a917b17..33e23a7a691f 100644
--- a/drivers/block/xen-blkback/blkback.c
+++ b/drivers/block/xen-blkback/blkback.c
@@ -595,8 +595,6 @@ int xen_blkif_schedule(void *arg)
 	unsigned long timeout;
 	int ret;
 
-	xen_blkif_get(blkif);
-
 	while (!kthread_should_stop()) {
 		if (try_to_freeze())
 			continue;
@@ -650,7 +648,6 @@ purge_gnt_list:
 		print_stats(blkif);
 
 	blkif->xenblkd = NULL;
-	xen_blkif_put(blkif);
 
 	return 0;
 }
diff --git a/drivers/block/xen-blkback/xenbus.c b/drivers/block/xen-blkback/xenbus.c
index 58f151e283ff..923308201375 100644
--- a/drivers/block/xen-blkback/xenbus.c
+++ b/drivers/block/xen-blkback/xenbus.c
@@ -221,7 +221,6 @@ static int xen_blkif_disconnect(struct xen_blkif *blkif)
 	if (blkif->xenblkd) {
 		kthread_stop(blkif->xenblkd);
 		wake_up(&blkif->shutdown_wq);
-		blkif->xenblkd = NULL;
 	}
 
 	/* The above kthread_stop() guarantees that at this point we
-- 
2.12.3