Re: [PATCH] net: decnet: Replace GFP_ATOMIC with GFP_KERNEL in dn_route_init

[Jia-Ju Bai]

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 <baijiaju1990@xxxxxxxxx>
> > ---
> >   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_mask--;
> >   		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