[PATCH v4] pvcalls-front: Avoid get_free_pages(GFP_KERNEL) under spinlock

[Wen Yang]

The problem is that we call this with a spin lock held.
The call tree is:
pvcalls_front_accept() holds bedata->socket_lock.
    -> create_active()
        -> __get_free_pages() uses GFP_KERNEL

The create_active() function is only called from pvcalls_front_accept()
with a spin_lock held, The allocation is not allowed to sleep and
GFP_KERNEL is not sufficient.

This issue was detected by using the Coccinelle software.

v2: Add a function doing the allocations which is called
    outside the lock and passing the allocated data to
    create_active().

v3: Use the matching deallocators i.e., free_page()
    and free_pages(), respectively.

v4: It would be better to pre-populate map (struct sock_mapping),
    rather than introducing one more new struct.

Suggested-by: Juergen Gross <jgross@xxxxxxxx>
Suggested-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Suggested-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
Signed-off-by: Wen Yang <wen.yang99@xxxxxxxxxx>
CC: Julia Lawall <julia.lawall@xxxxxxx>
CC: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
CC: Juergen Gross <jgross@xxxxxxxx>
CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
CC: xen-devel@xxxxxxxxxxxxxxxxxxxx
CC: linux-kernel@xxxxxxxxxxxxxxx
---
 drivers/xen/pvcalls-front.c | 57 ++++++++++++++++++++++++++++++-------
 1 file changed, 46 insertions(+), 11 deletions(-)

diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
index 77224d8f3e6f..555c9abdf58f 100644
--- a/drivers/xen/pvcalls-front.c
+++ b/drivers/xen/pvcalls-front.c
@@ -335,13 +335,18 @@ int pvcalls_front_socket(struct socket *sock)
 	return ret;
 }
 
-static int create_active(struct sock_mapping *map, int *evtchn)
+static void free_active_ring(struct sock_mapping *map)
 {
-	void *bytes;
-	int ret = -ENOMEM, irq = -1, i;
+	if (!map)
+		return;
+	free_pages((unsigned long)map->active.data.in,
+			map->active.ring->ring_order);
+	free_page((unsigned long)map->active.ring);
+}
 
-	*evtchn = -1;
-	init_waitqueue_head(&map->active.inflight_conn_req);
+static int alloc_active_ring(struct sock_mapping *map)
+{
+	void *bytes;
 
 	map->active.ring = (struct pvcalls_data_intf *)
 		__get_free_page(GFP_KERNEL | __GFP_ZERO);
@@ -352,6 +357,26 @@ static int create_active(struct sock_mapping *map, int *evtchn)
 					PVCALLS_RING_ORDER);
 	if (bytes == NULL)
 		goto out_error;
+	map->active.data.in = bytes;
+	map->active.data.out = bytes +
+		XEN_FLEX_RING_SIZE(PVCALLS_RING_ORDER);
+
+	return 0;
+
+out_error:
+	free_active_ring(map);
+	return -ENOMEM;
+}
+
+static int create_active(struct sock_mapping *map, int *evtchn)
+{
+	void *bytes;
+	int ret = -ENOMEM, irq = -1, i;
+
+	*evtchn = -1;
+	init_waitqueue_head(&map->active.inflight_conn_req);
+
+	bytes = map->active.data.in;
 	for (i = 0; i < (1 << PVCALLS_RING_ORDER); i++)
 		map->active.ring->ref[i] = gnttab_grant_foreign_access(
 			pvcalls_front_dev->otherend_id,
@@ -361,10 +386,6 @@ static int create_active(struct sock_mapping *map, int *evtchn)
 		pvcalls_front_dev->otherend_id,
 		pfn_to_gfn(virt_to_pfn((void *)map->active.ring)), 0);
 
-	map->active.data.in = bytes;
-	map->active.data.out = bytes +
-		XEN_FLEX_RING_SIZE(PVCALLS_RING_ORDER);
-
 	ret = xenbus_alloc_evtchn(pvcalls_front_dev, evtchn);
 	if (ret)
 		goto out_error;
@@ -385,8 +406,7 @@ static int create_active(struct sock_mapping *map, int *evtchn)
 out_error:
 	if (*evtchn >= 0)
 		xenbus_free_evtchn(pvcalls_front_dev, *evtchn);
-	free_pages((unsigned long)map->active.data.in, PVCALLS_RING_ORDER);
-	free_page((unsigned long)map->active.ring);
+	free_active_ring(map);
 	return ret;
 }
 
@@ -406,11 +426,17 @@ int pvcalls_front_connect(struct socket *sock, struct sockaddr *addr,
 		return PTR_ERR(map);
 
 	bedata = dev_get_drvdata(&pvcalls_front_dev->dev);
+	ret = alloc_active_ring(map);
+	if (ret < 0) {
+		pvcalls_exit_sock(sock);
+		return ret;
+	}
 
 	spin_lock(&bedata->socket_lock);
 	ret = get_request(bedata, &req_id);
 	if (ret < 0) {
 		spin_unlock(&bedata->socket_lock);
+		free_active_ring(map);
 		pvcalls_exit_sock(sock);
 		return ret;
 	}
@@ -780,12 +806,20 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
 		}
 	}
 
+	ret = alloc_active_ring(map);
+	if (ret < 0) {
+		clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
+				(void *)&map->passive.flags);
+		pvcalls_exit_sock(sock);
+		return ret;
+	}
 	spin_lock(&bedata->socket_lock);
 	ret = get_request(bedata, &req_id);
 	if (ret < 0) {
 		clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
 			  (void *)&map->passive.flags);
 		spin_unlock(&bedata->socket_lock);
+		free_active_ring(map);
 		pvcalls_exit_sock(sock);
 		return ret;
 	}
@@ -794,6 +828,7 @@ int pvcalls_front_accept(struct socket *sock, struct socket *newsock, int flags)
 		clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
 			  (void *)&map->passive.flags);
 		spin_unlock(&bedata->socket_lock);
+		free_active_ring(map);
 		pvcalls_exit_sock(sock);
 		return -ENOMEM;
 	}
-- 
2.19.1