linux-kernel - [PATCH] pvcalls-front: Use GFP_ATOMIC under spin

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Date:   Thu, 29 Nov 2018 20:01:01 +0800
From:   Wen Yang <wen.yang99@....com.cn>
To:     boris.ostrovsky@...cle.com, jgross@...e.com, sstabellini@...nel.org
Cc:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        zhong.weidong@....com.cn, Wen Yang <wen.yang99@....com.cn>,
        Julia Lawall <julia.lawall@...6.fr>
Subject: [PATCH] pvcalls-front: Use GFP_ATOMIC under spin_lock

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@....com.cn>
CC: Julia Lawall <julia.lawall@...6.fr>
CC: Boris Ostrovsky <boris.ostrovsky@...cle.com>
CC: Juergen Gross <jgross@...e.com>
CC: Stefano Stabellini <sstabellini@...nel.org>
CC: xen-devel@...ts.xenproject.org
CC: linux-kernel@...r.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