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

Julia Lawall
2010-05-30T20:50:24Z

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On Sun, 30 May 2010, Eric Dumazet wrote:

> 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 ?

I think the proposed patch does not work, because the for loop overwrites
p. That use of p looks like it is completely local to the for loop, so
perhaps a new variable p1 could be added to be used there?

julia

> 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;
> }
>
>
>
> --
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