Re: Subject: [PATCH] net/ipv6: Use GFP_ATOMIC when a lock is held

Eric Dumazet
2010-05-30T20:11:34Z

Le dimanche 30 mai 2010 à 21:48 +0200, Julia Lawall a écrit :
> From: Julia Lawall <julia@diku.dk>
>
> A spin lock is taken near the beginning of the enclosing function.
>
> The semantic patch that makes this change is as follows:
> (http://coccinelle.lip6.fr/)
>
> // <smpl>
> @@
> @@
>
> spin_lock(...)
> ... when != spin_unlock(...)
> -GFP_KERNEL
> +GFP_ATOMIC
> // </smpl>
>
> Signed-off-by: Julia Lawall <julia@diku.dk>
>
> ---
> net/ipv6/sit.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff -u -p a/net/ipv6/sit.c b/net/ipv6/sit.c
> --- a/net/ipv6/sit.c
> +++ b/net/ipv6/sit.c
> @@ -358,7 +358,7 @@ ipip6_tunnel_add_prl(struct ip_tunnel *t
> goto out;
> }
>
> - p = kzalloc(sizeof(struct ip_tunnel_prl_entry), GFP_KERNEL);
> + p = kzalloc(sizeof(struct ip_tunnel_prl_entry), GFP_ATOMIC);
> if (!p) {
> err = -ENOBUFS;
> goto out;

Nice catch, but what about allocating this outside of the locked
section ?

diff --git a/net/ipv6/sit.c b/net/ipv6/sit.c
index e51e650..ff3dd84 100644
--- a/net/ipv6/sit.c
+++ b/net/ipv6/sit.c
@@ -340,6 +340,10 @@ ipip6_tunnel_add_prl(struct ip_tunnel *t, struct ip_tunnel_prl *a, int chg)
if (a->addr == htonl(INADDR_ANY))
return -EINVAL;

+ p = kzalloc(sizeof(struct ip_tunnel_prl_entry), GFP_KERNEL);
+ if (!p)
+ return -ENOBUFS;
+
spin_lock(&ipip6_prl_lock);

for (p = t->prl; p; p = p->next) {
@@ -358,19 +362,16 @@ ipip6_tunnel_add_prl(struct ip_tunnel *t, struct ip_tunnel_prl *a, int chg)
goto out;
}

- p = kzalloc(sizeof(struct ip_tunnel_prl_entry), GFP_KERNEL);
- if (!p) {
- err = -ENOBUFS;
- goto out;
- }

p->next = t->prl;
p->addr = a->addr;
p->flags = a->flags;
t->prl_count++;
rcu_assign_pointer(t->prl, p);
+ p = NULL;
out:
spin_unlock(&ipip6_prl_lock);
+ kfree(p);
return err;
}