[Xen-devel] [PATCH v6] 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().

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.

v5: Since allocating the data outside of this call it should also
    be freed outside, when create_active() fails.
    Move kzalloc(sizeof(*map2), GFP_ATOMIC) outside spinlock and
    use GFP_KERNEL instead.

v6: Drop the superfluous calls.

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 | 81 +++++++++++++++++++++++++++----------
 1 file changed, 59 insertions(+), 22 deletions(-)

diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
index 77224d8f3e6f..3324fcc4596d 100644
--- a/drivers/xen/pvcalls-front.c
+++ b/drivers/xen/pvcalls-front.c
@@ -335,6 +335,39 @@ int pvcalls_front_socket(struct socket *sock)
        return ret;
 }
 
+static void free_active_ring(struct sock_mapping *map)
+{
+       free_pages((unsigned long)map->active.data.in,
+                       map->active.ring->ring_order);
+       free_page((unsigned long)map->active.ring);
+}
+
+static int alloc_active_ring(struct sock_mapping *map)
+{
+       void *bytes;
+
+       map->active.ring = (struct pvcalls_data_intf *)
+               get_zeroed_page(GFP_KERNEL);
+       if (!map->active.ring)
+               goto out;
+
+       map->active.ring->ring_order = PVCALLS_RING_ORDER;
+       bytes = (void *)__get_free_pages(GFP_KERNEL | __GFP_ZERO,
+                                       PVCALLS_RING_ORDER);
+       if (!bytes)
+               goto out;
+
+       map->active.data.in = bytes;
+       map->active.data.out = bytes +
+               XEN_FLEX_RING_SIZE(PVCALLS_RING_ORDER);
+
+       return 0;
+
+out:
+       free_active_ring(map);
+       return -ENOMEM;
+}
+
 static int create_active(struct sock_mapping *map, int *evtchn)
 {
        void *bytes;
@@ -343,15 +376,7 @@ 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;
+       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 +406,6 @@ 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);
        return ret;
 }
 
@@ -406,17 +425,24 @@ 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;
        }
        ret = create_active(map, &evtchn);
        if (ret < 0) {
                spin_unlock(&bedata->socket_lock);
+               free_active_ring(map);
                pvcalls_exit_sock(sock);
                return ret;
        }
@@ -780,25 +806,36 @@ int pvcalls_front_accept(struct socket *sock, struct 
socket *newsock, int flags)
                }
        }
 
-       spin_lock(&bedata->socket_lock);
-       ret = get_request(bedata, &req_id);
-       if (ret < 0) {
+       map2 = kzalloc(sizeof(*map2), GFP_KERNEL);
+       if (map2 == NULL) {
                clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
                          (void *)&map->passive.flags);
-               spin_unlock(&bedata->socket_lock);
+               pvcalls_exit_sock(sock);
+               return -ENOMEM;
+       }
+       ret = alloc_active_ring(map2);
+       if (ret < 0) {
+               clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
+                               (void *)&map->passive.flags);
+               kfree(map2);
                pvcalls_exit_sock(sock);
                return ret;
        }
-       map2 = kzalloc(sizeof(*map2), GFP_ATOMIC);
-       if (map2 == NULL) {
+       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(map2);
+               kfree(map2);
                pvcalls_exit_sock(sock);
-               return -ENOMEM;
+               return ret;
        }
+
        ret = create_active(map2, &evtchn);
        if (ret < 0) {
+               free_active_ring(map2);
                kfree(map2);
                clear_bit(PVCALLS_FLAG_ACCEPT_INFLIGHT,
                          (void *)&map->passive.flags);
-- 
2.19.1


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel