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@xxxxxxxxx> 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@xxxxxxxxx>
> > ---
> > 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