[PATCH] block: aoenet: Replace GFP_ATOMIC with GFP_KERNEL in aoenet_rcv

[PATCH] block: aoenet: Replace GFP_ATOMIC with GFP_KERNEL in aoenet_rcv

[Jia-Ju Bai]

After checking all possible call chains to aoenet_rcv(),
my tool finds that aoenet_rcv() is never called in atomic context, 
namely never in an interrupt handler or holding a spinlock.
Thus GFP_ATOMIC is not necessary, and it can be replaced with GFP_KERNEL.

This is found by a static analysis tool named DCNS written by myself.

Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
---
 drivers/block/aoe/aoenet.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/block/aoe/aoenet.c b/drivers/block/aoe/aoenet.c
index 63773a9..d5fff7a 100644
--- a/drivers/block/aoe/aoenet.c
+++ b/drivers/block/aoe/aoenet.c
@@ -138,7 +138,7 @@ static int __init aoe_iflist_setup(char *str)
 	if (dev_net(ifp) != &init_net)
 		goto exit;
 
-	skb = skb_share_check(skb, GFP_ATOMIC);
+	skb = skb_share_check(skb, GFP_KERNEL);
 	if (skb == NULL)
 		return 0;
 	if (!is_aoe_netif(ifp))
-- 
1.7.9.5

Re: [PATCH] block: aoenet: Replace GFP_ATOMIC with GFP_KERNEL in aoenet_rcv

[Ed Cashin]

If the tool cannot tell whether the protected state is manipulated by *another* piece of code called in atomic context, then it's insufficient.

> On Jan 26, 2018, at 4:37 AM, Jia-Ju Bai <baijiaju1990@gmail.com> wrote:
> 
> After checking all possible call chains to aoenet_rcv(),
> my tool finds that aoenet_rcv() is never called in atomic context, 
> namely never in an interrupt handler or holding a spinlock.
> Thus GFP_ATOMIC is not necessary, and it can be replaced with GFP_KERNEL.
> 
> This is found by a static analysis tool named DCNS written by myself.
> 
> Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
> ---
> drivers/block/aoe/aoenet.c |    2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/block/aoe/aoenet.c b/drivers/block/aoe/aoenet.c
> index 63773a9..d5fff7a 100644
> --- a/drivers/block/aoe/aoenet.c
> +++ b/drivers/block/aoe/aoenet.c
> @@ -138,7 +138,7 @@ static int __init aoe_iflist_setup(char *str)
>    if (dev_net(ifp) != &init_net)
>        goto exit;
> 
> -    skb = skb_share_check(skb, GFP_ATOMIC);
> +    skb = skb_share_check(skb, GFP_KERNEL);
>    if (skb == NULL)
>        return 0;
>    if (!is_aoe_netif(ifp))
> -- 
> 1.7.9.5
> 

Re: [PATCH] block: aoenet: Replace GFP_ATOMIC with GFP_KERNEL in aoenet_rcv

[Jia-Ju Bai]

On 2018/1/28 1:48, Ed Cashin wrote:
> If the tool cannot tell whether the protected state is manipulated by *another* piece of code called in atomic context, then it's insufficient.
>
>> On Jan 26, 2018, at 4:37 AM, Jia-Ju Bai <baijiaju1990@gmail.com> wrote:
>>
>> After checking all possible call chains to aoenet_rcv(),
>> my tool finds that aoenet_rcv() is never called in atomic context,
>> namely never in an interrupt handler or holding a spinlock.
>> Thus GFP_ATOMIC is not necessary, and it can be replaced with GFP_KERNEL.
>>
>> This is found by a static analysis tool named DCNS written by myself.
>>
>> Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
>> ---
>> drivers/block/aoe/aoenet.c |    2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/block/aoe/aoenet.c b/drivers/block/aoe/aoenet.c
>> index 63773a9..d5fff7a 100644
>> --- a/drivers/block/aoe/aoenet.c
>> +++ b/drivers/block/aoe/aoenet.c
>> @@ -138,7 +138,7 @@ static int __init aoe_iflist_setup(char *str)
>>     if (dev_net(ifp) != &init_net)
>>         goto exit;
>>
>> -    skb = skb_share_check(skb, GFP_ATOMIC);
>> +    skb = skb_share_check(skb, GFP_KERNEL);
>>     if (skb == NULL)
>>         return 0;
>>     if (!is_aoe_netif(ifp))
>> -- 
>> 1.7.9.5
>>
>>

Sorry, I find my report is false positive after I manually check the code.
aoenet_rcv() is used as function pointer via "->func", and it is called 
in dev_queue_xmit_nit() in net/core/dev.c.
dev_queue_xmit_nit() calls a rcu_read_lock() before it calls 
pt_prev->func().
Thus it is right to use GFP_ATOMIC in aoenet_rcv().
Sorry again for my incorrect report...

Thanks,
Jia-Ju Bai

Re: [PATCH] block: aoenet: Replace GFP_ATOMIC with GFP_KERNEL in aoenet_rcv

[Ed Cashin]

Good luck in your efforts, and thanks for your work on static analysis.

> On Jan 27, 2018, at 9:12 PM, Jia-Ju Bai <baijiaju1990@gmail.com> wrote:
> 
> 
> 
>> On 2018/1/28 1:48, Ed Cashin wrote:
>> If the tool cannot tell whether the protected state is manipulated by *another* piece of code called in atomic context, then it's insufficient.
>> 
>>> On Jan 26, 2018, at 4:37 AM, Jia-Ju Bai <baijiaju1990@gmail.com> wrote:
>>> 
>>> After checking all possible call chains to aoenet_rcv(),
>>> my tool finds that aoenet_rcv() is never called in atomic context,
>>> namely never in an interrupt handler or holding a spinlock.
>>> Thus GFP_ATOMIC is not necessary, and it can be replaced with GFP_KERNEL.
>>> 
>>> This is found by a static analysis tool named DCNS written by myself.
>>> 
>>> Signed-off-by: Jia-Ju Bai <baijiaju1990@gmail.com>
>>> ---
>>> drivers/block/aoe/aoenet.c |    2 +-
>>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>> 
>>> diff --git a/drivers/block/aoe/aoenet.c b/drivers/block/aoe/aoenet.c
>>> index 63773a9..d5fff7a 100644
>>> --- a/drivers/block/aoe/aoenet.c
>>> +++ b/drivers/block/aoe/aoenet.c
>>> @@ -138,7 +138,7 @@ static int __init aoe_iflist_setup(char *str)
>>>    if (dev_net(ifp) != &init_net)
>>>        goto exit;
>>> 
>>> -    skb = skb_share_check(skb, GFP_ATOMIC);
>>> +    skb = skb_share_check(skb, GFP_KERNEL);
>>>    if (skb == NULL)
>>>        return 0;
>>>    if (!is_aoe_netif(ifp))
>>> -- 
>>> 1.7.9.5
>>> 
>>> 
> 
> Sorry, I find my report is false positive after I manually check the code.
> aoenet_rcv() is used as function pointer via "->func", and it is called in dev_queue_xmit_nit() in net/core/dev.c.
> dev_queue_xmit_nit() calls a rcu_read_lock() before it calls pt_prev->func().
> Thus it is right to use GFP_ATOMIC in aoenet_rcv().
> Sorry again for my incorrect report...
> 
> Thanks,
> Jia-Ju Bai