[Xen-devel] [PATCH v2] pvcalls-front: Avoid __get_free_pages(GFP_KERNEL) under spinlock

[Wen Yang <wen.yang99@xxxxxxxxxx>]

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().

Suggested-by: Juergen Gross <jgross@xxxxxxxx>
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 | 71 ++++++++++++++++++++++++++++++-------
 1 file changed, 59 insertions(+), 12 deletions(-)

diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
index 2f11ca72a281..cc92af31807f 100644
--- a/drivers/xen/pvcalls-front.c
+++ b/drivers/xen/pvcalls-front.c
@@ -335,7 +335,43 @@ int pvcalls_front_socket(struct socket *sock)
        return ret;
 }
 
-static int create_active(struct sock_mapping *map, int *evtchn)
+struct sock_mapping_active_ring {
+       struct pvcalls_data_intf *ring;
+       RING_IDX ring_order;
+       void *bytes;
+};
+
+static int alloc_active_ring(struct sock_mapping_active_ring *active_ring)
+{
+       active_ring->ring = NULL;
+       active_ring->bytes = NULL;
+
+       active_ring->ring = (struct pvcalls_data_intf *)
+               __get_free_page(GFP_KERNEL | __GFP_ZERO);
+       if (active_ring->ring == NULL)
+               goto out_error;
+       active_ring->ring_order = PVCALLS_RING_ORDER;
+       active_ring->bytes = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO,
+                       PVCALLS_RING_ORDER);
+       if (active_ring->bytes == NULL)
+               goto out_error;
+
+       return 0;
+
+out_error:
+       kfree(active_ring->bytes);
+       kfree(active_ring->ring);
+       return -ENOMEM;
+}
+
+static void free_active_ring(struct sock_mapping_active_ring *active_ring)
+{
+       free_pages((unsigned long)active_ring->bytes, active_ring->ring_order);
+       free_page((unsigned long)active_ring->ring);
+}
+
+static int create_active(struct sock_mapping *map, int *evtchn,
+               struct sock_mapping_active_ring *active_ring)
 {
        void *bytes;
        int ret = -ENOMEM, irq = -1, i;
@@ -343,15 +379,9 @@ static int create_active(struct sock_mapping *map, int 
*evtchn)
        *evtchn = -1;
        init_waitqueue_head(&map->active.inflight_conn_req);
 
-       map->active.ring = (struct pvcalls_data_intf *)
-               __get_free_page(GFP_KERNEL | __GFP_ZERO);
-       if (map->active.ring == NULL)
-               goto out_error;
-       map->active.ring->ring_order = PVCALLS_RING_ORDER;
-       bytes = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO,
-                                       PVCALLS_RING_ORDER);
-       if (bytes == NULL)
-               goto out_error;
+       map->active.ring = active_ring->ring;
+       map->active.ring->ring_order = active_ring->ring_order;
+       bytes = active_ring->bytes;
        for (i = 0; i < (1 << PVCALLS_RING_ORDER); i++)
                map->active.ring->ref[i] = gnttab_grant_foreign_access(
                        pvcalls_front_dev->otherend_id,
@@ -397,6 +427,7 @@ int pvcalls_front_connect(struct socket *sock, struct 
sockaddr *addr,
        struct sock_mapping *map = NULL;
        struct xen_pvcalls_request *req;
        int notify, req_id, ret, evtchn;
+       struct sock_mapping_active_ring active_ring;
 
        if (addr->sa_family != AF_INET || sock->type != SOCK_STREAM)
                return -EOPNOTSUPP;
@@ -406,15 +437,21 @@ 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(&active_ring);
+       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(&active_ring);
                pvcalls_exit_sock(sock);
                return ret;
        }
-       ret = create_active(map, &evtchn);
+       ret = create_active(map, &evtchn, &active_ring);
        if (ret < 0) {
                spin_unlock(&bedata->socket_lock);
                pvcalls_exit_sock(sock);
@@ -744,6 +781,7 @@ int pvcalls_front_accept(struct socket *sock, struct socket 
*newsock, int flags)
        struct sock_mapping *map2 = NULL;
        struct xen_pvcalls_request *req;
        int notify, req_id, ret, evtchn, nonblock;
+       struct sock_mapping_active_ring active_ring;
 
        map = pvcalls_enter_sock(sock);
        if (IS_ERR(map))
@@ -780,12 +818,20 @@ int pvcalls_front_accept(struct socket *sock, struct 
socket *newsock, int flags)
                }
        }
 
+       ret = alloc_active_ring(&active_ring);
+       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(&active_ring);
                pvcalls_exit_sock(sock);
                return ret;
        }
@@ -794,10 +840,11 @@ 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(&active_ring);
                pvcalls_exit_sock(sock);
                return -ENOMEM;
        }
-       ret = create_active(map2, &evtchn);
+       ret = create_active(map2, &evtchn, &active_ring);
        if (ret < 0) {
                kfree(map2);
                clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
-- 
2.19.1


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