4 files changed, 56 insertions, 4 deletions

diff --git a/drivers/xen/xenbus/xenbus_comms.c b/drivers/xen/xenbus/xenbus_comms.c
index d239fc3c5e3d..eb5151fc8efa 100644
--- a/drivers/xen/xenbus/xenbus_comms.c
+++ b/drivers/xen/xenbus/xenbus_comms.c
@@ -313,6 +313,8 @@ static int process_msg(void)
 			req->msg.type = state.msg.type;
 			req->msg.len = state.msg.len;
 			req->body = state.body;
+			/* write body, then update state */
+			virt_wmb();
 			req->state = xb_req_state_got_reply;
 			req->cb(req);
 		} else
@@ -395,6 +397,8 @@ static int process_writes(void)
 	if (state.req->state == xb_req_state_aborted)
 		kfree(state.req);
 	else {
+		/* write err, then update state */
+		virt_wmb();
 		state.req->state = xb_req_state_got_reply;
 		wake_up(&state.req->wq);
 	}
diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
index 378486b79f96..8c4d05b687b7 100644
--- a/drivers/xen/xenbus/xenbus_probe.c
+++ b/drivers/xen/xenbus/xenbus_probe.c
@@ -239,7 +239,9 @@ int xenbus_dev_probe(struct device *_dev)
 		goto fail;
 	}
 
+	down(&dev->reclaim_sem);
 	err = drv->probe(dev, id);
+	up(&dev->reclaim_sem);
 	if (err)
 		goto fail_put;
 
@@ -268,8 +270,11 @@ int xenbus_dev_remove(struct device *_dev)
 
 	free_otherend_watch(dev);
 
-	if (drv->remove)
+	if (drv->remove) {
+		down(&dev->reclaim_sem);
 		drv->remove(dev);
+		up(&dev->reclaim_sem);
+	}
 
 	module_put(drv->driver.owner);
 
@@ -468,6 +473,7 @@ int xenbus_probe_node(struct xen_bus_type *bus,
 		goto fail;
 
 	dev_set_name(&xendev->dev, "%s", devname);
+	sema_init(&xendev->reclaim_sem, 1);
 
 	/* Register with generic device framework. */
 	err = device_register(&xendev->dev);
diff --git a/drivers/xen/xenbus/xenbus_probe_backend.c b/drivers/xen/xenbus/xenbus_probe_backend.c
index 14876faff3b0..9b2fbe69bccc 100644
--- a/drivers/xen/xenbus/xenbus_probe_backend.c
+++ b/drivers/xen/xenbus/xenbus_probe_backend.c
@@ -45,6 +45,7 @@
 #include <linux/mm.h>
 #include <linux/notifier.h>
 #include <linux/export.h>
+#include <linux/semaphore.h>
 
 #include <asm/page.h>
 #include <asm/pgtable.h>
@@ -247,6 +248,41 @@ static int backend_probe_and_watch(struct notifier_block *notifier,
 	return NOTIFY_DONE;
 }
 
+static int backend_reclaim_memory(struct device *dev, void *data)
+{
+	const struct xenbus_driver *drv;
+	struct xenbus_device *xdev;
+
+	if (!dev->driver)
+		return 0;
+	drv = to_xenbus_driver(dev->driver);
+	if (drv && drv->reclaim_memory) {
+		xdev = to_xenbus_device(dev);
+		if (down_trylock(&xdev->reclaim_sem))
+			return 0;
+		drv->reclaim_memory(xdev);
+		up(&xdev->reclaim_sem);
+	}
+	return 0;
+}
+
+/*
+ * Returns 0 always because we are using shrinker to only detect memory
+ * pressure.
+ */
+static unsigned long backend_shrink_memory_count(struct shrinker *shrinker,
+				struct shrink_control *sc)
+{
+	bus_for_each_dev(&xenbus_backend.bus, NULL, NULL,
+			backend_reclaim_memory);
+	return 0;
+}
+
+static struct shrinker backend_memory_shrinker = {
+	.count_objects = backend_shrink_memory_count,
+	.seeks = DEFAULT_SEEKS,
+};
+
 static int __init xenbus_probe_backend_init(void)
 {
 	static struct notifier_block xenstore_notifier = {
@@ -263,6 +299,9 @@ static int __init xenbus_probe_backend_init(void)
 
 	register_xenstore_notifier(&xenstore_notifier);
 
+	if (register_shrinker(&backend_memory_shrinker))
+		pr_warn("shrinker registration failed\n");
+
 	return 0;
 }
 subsys_initcall(xenbus_probe_backend_init);
diff --git a/drivers/xen/xenbus/xenbus_xs.c b/drivers/xen/xenbus/xenbus_xs.c
index ddc18da61834..3a06eb699f33 100644
--- a/drivers/xen/xenbus/xenbus_xs.c
+++ b/drivers/xen/xenbus/xenbus_xs.c
@@ -191,8 +191,11 @@ static bool xenbus_ok(void)
 
 static bool test_reply(struct xb_req_data *req)
 {
-	if (req->state == xb_req_state_got_reply || !xenbus_ok())
+	if (req->state == xb_req_state_got_reply || !xenbus_ok()) {
+		/* read req->state before all other fields */
+		virt_rmb();
 		return true;
+	}
 
 	/* Make sure to reread req->state each time. */
 	barrier();
@@ -202,7 +205,7 @@ static bool test_reply(struct xb_req_data *req)
 
 static void *read_reply(struct xb_req_data *req)
 {
-	while (req->state != xb_req_state_got_reply) {
+	do {
 		wait_event(req->wq, test_reply(req));
 
 		if (!xenbus_ok())
@@ -216,7 +219,7 @@ static void *read_reply(struct xb_req_data *req)
 		if (req->err)
 			return ERR_PTR(req->err);
 
-	}
+	} while (req->state != xb_req_state_got_reply);
 
 	return req->body;
 }