On 2018/4/9 22:44, Eric Dumazet wrote:

On 04/09/2018 07:10 AM, Jia-Ju Bai wrote:
dn_route_init() is never called in atomic context.

The call chain ending up at dn_route_init() is:
[1] dn_route_init() <- decnet_init()
decnet_init() is only set as a parameter of module_init().

Despite never getting called from atomic context,
dn_route_init() calls __get_free_pages() with GFP_ATOMIC,
which waits busily for allocation.
GFP_ATOMIC is not necessary and can be replaced with GFP_KERNEL,
to avoid busy waiting and improve the possibility of sucessful allocation.

This is found by a static analysis tool named DCNS written by myself.
And I also manually check it.

Signed-off-by: Jia-Ju Bai <baijiaju1...@gmail.com>
  net/decnet/dn_route.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/decnet/dn_route.c b/net/decnet/dn_route.c
index 0bd3afd..59ed12a 100644
--- a/net/decnet/dn_route.c
+++ b/net/decnet/dn_route.c
@@ -1898,7 +1898,7 @@ void __init dn_route_init(void)
                while(dn_rt_hash_mask & (dn_rt_hash_mask - 1))
                dn_rt_hash_table = (struct dn_rt_hash_bucket *)
-                       __get_free_pages(GFP_ATOMIC, order);
+                       __get_free_pages(GFP_KERNEL, order);
        } while (dn_rt_hash_table == NULL && --order > 0);
if (!dn_rt_hash_table)

This might OOM under pressure.

Sorry, I do not understand this.
Could you please explain the reason?

This would need __GFP_NOWARN | __GFP_NORETRY  I guess, and would target net-next

Do you mean
__get_free_pages(__GFP_NOWARN | __GFP_NORETRY) or
__get_free_pages(__GFP_NOWARN | __GFP_NORETRY | GFP_KERNEL)?

Best wishes,
Jia-Ju Bai

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