[PATCH] pvcalls-front: Use GFP_ATOMIC under spin_lock

[PATCH] pvcalls-front: Use GFP_ATOMIC under spin_lock

[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, it has to be ATOMIC.

This issue was detected by using the Coccinelle software.

Signed-off-by: Wen Yang <wen.yang99@zte.com.cn>
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
---
 drivers/xen/pvcalls-front.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/xen/pvcalls-front.c b/drivers/xen/pvcalls-front.c
index 2f11ca72a281..f2bbc06a0f7f 100644
--- a/drivers/xen/pvcalls-front.c
+++ b/drivers/xen/pvcalls-front.c
@@ -344,11 +344,11 @@ static int create_active(struct sock_mapping *map, int *evtchn)
 	init_waitqueue_head(&map->active.inflight_conn_req);
 
 	map->active.ring = (struct pvcalls_data_intf *)
-		__get_free_page(GFP_KERNEL | __GFP_ZERO);
+		__get_free_page(GFP_ATOMIC | __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,
+	bytes = (void *)__get_free_pages(GFP_ATOMIC | __GFP_ZERO,
 					PVCALLS_RING_ORDER);
 	if (bytes == NULL)
 		goto out_error;
-- 
2.19.1

Re: [PATCH] pvcalls-front: Use GFP_ATOMIC under spin_lock

[Juergen Gross]

On 29/11/2018 13:01, Wen Yang wrote:
> 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, it has to be ATOMIC.

I'd rather have a function doing the allocations which is called
outside the lock and either passing the allocated data to
create_active() or hook it into map in the allocation function.


Juergen