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Subject[PATCH 4.20 063/183] pvcalls-front: Avoid get_free_pages(GFP_KERNEL) under spinlock
Date
4.20-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit 9f51c05dc41a6d69423e3d03d18eb7ab22f9ec19 ]

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@suse.com>
Suggested-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Suggested-by: Stefano Stabellini <sstabellini@kernel.org>
Signed-off-by: Wen Yang <wen.yang99@zte.com.cn>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>
CC: Julia Lawall <julia.lawall@lip6.fr>
CC: Boris Ostrovsky <boris.ostrovsky@oracle.com>
CC: Juergen Gross <jgross@suse.com>
CC: Stefano Stabellini <sstabellini@kernel.org>
CC: xen-devel@lists.xenproject.org
CC: linux-kernel@vger.kernel.org
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
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 01588582ae663..6357160d466ab 100644
--- a/drivers/xen/pvcalls-front.c
+++ b/drivers/xen/pvcalls-front.c
@@ -341,6 +341,39 @@ 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;
@@ -349,15 +382,7 @@ 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,
@@ -367,10 +392,6 @@ 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;
@@ -391,8 +412,6 @@ 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;
}

@@ -412,17 +431,24 @@ 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;
}
@@ -784,25 +810,36 @@ 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


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