[PATCH] xen: Fix two possible sleep-in-atomic-context bugs in create_active()

[Jia-Ju Bai]

The driver may sleep with holding a spinlock.
The function call paths (from bottom to top) in Linux-4.16.7 are:

[FUNC] __get_free_pages(GFP_KERNEL)
drivers/xen/pvcalls-front.c, 351: __get_free_pages in create_active
drivers/xen/pvcalls-front.c, 800: create_active in pvcalls_front_accept
drivers/xen/pvcalls-front.c, 783: spin_lock in pvcalls_front_accept

[FUNC] __get_free_pages(GFP_KERNEL)
drivers/xen/pvcalls-front.c, 347: __get_free_pages in create_active
drivers/xen/pvcalls-front.c, 800: create_active in pvcalls_front_accept
drivers/xen/pvcalls-front.c, 783: spin_lock in pvcalls_front_accept

To fix these bugs, GFP_KERNEL is replaced with GFP_ATOMIC.

These bugs are found by my static analysis tool (DSAC-2) and checked by my
code review.

Signed-off-by: Jia-Ju Bai <baijiaju1990@xxxxxxxxx>
---
 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;
-- 
2.17.0