[PATCH] net: dccp: Replace GFP_ATOMIC with GFP_KERNEL in dccp_init

[PATCH] net: dccp: Replace GFP_ATOMIC with GFP_KERNEL in dccp_init

[Jia-Ju Bai]

dccp_init() is never called in atomic context.
This function is only set as a parameter of module_init().

Despite never getting called from atomic context,
dccp_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 <baijiaju1990@gmail.com>
---
 net/dccp/proto.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/dccp/proto.c b/net/dccp/proto.c
index b68168f..f63ba93 100644
--- a/net/dccp/proto.c
+++ b/net/dccp/proto.c
@@ -1159,7 +1159,7 @@ static int __init dccp_init(void)
 			hash_size--;
 		dccp_hashinfo.ehash_mask = hash_size - 1;
 		dccp_hashinfo.ehash = (struct inet_ehash_bucket *)
-			__get_free_pages(GFP_ATOMIC|__GFP_NOWARN, ehash_order);
+			__get_free_pages(GFP_KERNEL|__GFP_NOWARN, ehash_order);
 	} while (!dccp_hashinfo.ehash && --ehash_order > 0);
 
 	if (!dccp_hashinfo.ehash) {
@@ -1182,7 +1182,7 @@ static int __init dccp_init(void)
 		    bhash_order > 0)
 			continue;
 		dccp_hashinfo.bhash = (struct inet_bind_hashbucket *)
-			__get_free_pages(GFP_ATOMIC|__GFP_NOWARN, bhash_order);
+			__get_free_pages(GFP_KERNEL|__GFP_NOWARN, bhash_order);
 	} while (!dccp_hashinfo.bhash && --bhash_order >= 0);
 
 	if (!dccp_hashinfo.bhash) {
-- 
1.9.1

Re: [PATCH] net: dccp: Replace GFP_ATOMIC with GFP_KERNEL in dccp_init

[Eric Dumazet]

On 04/09/2018 07:10 AM, Jia-Ju Bai wrote:
> dccp_init() is never called in atomic context.
> This function is only set as a parameter of module_init().
> 
> Despite never getting called from atomic context,
> dccp_init() calls __get_free_pages() with GFP_ATOMIC,
> which waits busily for allocation.

What do you mean by "waits busily" ?

GFP_ATOMIC does not sleep, does not wait.

> 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 <baijiaju1990@gmail.com>
> ---

Re: [PATCH] net: dccp: Replace GFP_ATOMIC with GFP_KERNEL in dccp_init

[Jia-Ju Bai]

On 2018/4/9 22:42, Eric Dumazet wrote:
>
> On 04/09/2018 07:10 AM, Jia-Ju Bai wrote:
>> dccp_init() is never called in atomic context.
>> This function is only set as a parameter of module_init().
>>
>> Despite never getting called from atomic context,
>> dccp_init() calls __get_free_pages() with GFP_ATOMIC,
>> which waits busily for allocation.
> What do you mean by "waits busily" ?
>
> GFP_ATOMIC does not sleep, does not wait.

Sorry, I should modify it to "does not sleep".
Do you think it is okay?


Best wishes,
Jia-Ju Bai