netdev - Re: [PATCH v2 net] ipv4: do not use this_cpu

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Message-ID: <CA+mtBx9U1EVmRi4amqVT=MMUvMSqo5907yzM0ytkQNvT74Gu2Q@mail.gmail.com>
Date:	Mon, 22 Sep 2014 11:44:02 -0700
From:	Tom Herbert <therbert@...gle.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Stephen Hemminger <stephen@...workplumber.org>,
	David Miller <davem@...emloft.net>,
	Linux Netdev List <netdev@...r.kernel.org>,
	joe9mail@...il.com
Subject: Re: [PATCH v2 net] ipv4: do not use this_cpu_ptr() in preemptible context

On Mon, Sep 22, 2014 at 10:38 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> From: Eric Dumazet <edumazet@...gle.com>
>
> this_cpu_ptr() in preemptible context is generally bad
>
> Sep 22 05:05:55 br kernel: [   94.608310] BUG: using smp_processor_id()
> in
> preemptible [00000000] code: ip/2261
> Sep 22 05:05:55 br kernel: [   94.608316] caller is
> tunnel_dst_set.isra.28+0x20/0x60 [ip_tunnel]
> Sep 22 05:05:55 br kernel: [   94.608319] CPU: 3 PID: 2261 Comm: ip Not
> tainted
> 3.17.0-rc5 #82
>
> We can simply use raw_cpu_ptr(), as preemption is safe in these
> contexts.
>
> Should fix https://bugzilla.kernel.org/show_bug.cgi?id=84991
>
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>
> Reported-by: Joe <joe9mail@...il.com>
> Fixes: 9a4aa9af447f ("ipv4: Use percpu Cache route in IP tunnels")

Acked-by: Tom Herbert <therbert@...gle.com>

> ---
> v2: use latest and shiny raw_cpu_ptr(), as it seems the latest
> incantation of ever changing percpu interface.
>
>  net/ipv4/ip_tunnel.c |    4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv4/ip_tunnel.c b/net/ipv4/ip_tunnel.c
> index afed1aac2638..bd41dd1948b6 100644
> --- a/net/ipv4/ip_tunnel.c
> +++ b/net/ipv4/ip_tunnel.c
> @@ -79,10 +79,10 @@ static void __tunnel_dst_set(struct ip_tunnel_dst *idst,
>         idst->saddr = saddr;
>  }
>
> -static void tunnel_dst_set(struct ip_tunnel *t,
> +static noinline void tunnel_dst_set(struct ip_tunnel *t,
>                            struct dst_entry *dst, __be32 saddr)
>  {
> -       __tunnel_dst_set(this_cpu_ptr(t->dst_cache), dst, saddr);
> +       __tunnel_dst_set(raw_cpu_ptr(t->dst_cache), dst, saddr);
>  }
>
>  static void tunnel_dst_reset(struct ip_tunnel *t)
> @@ -106,7 +106,7 @@ static struct rtable *tunnel_rtable_get(struct ip_tunnel *t,
>         struct dst_entry *dst;
>
>         rcu_read_lock();
> -       idst = this_cpu_ptr(t->dst_cache);
> +       idst = raw_cpu_ptr(t->dst_cache);
>         dst = rcu_dereference(idst->dst);
>         if (dst && !atomic_inc_not_zero(&dst->__refcnt))
>                 dst = NULL;
>
>
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