netdev - Re: [PATCH net] netns: fix GFP flags in rtnl_net

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Date:   Wed, 23 Oct 2019 18:06:25 -0700
From:   Pravin Shelar <pshelar@....org>
To:     Guillaume Nault <gnault@...hat.com>
Cc:     David Miller <davem@...emloft.net>,
        Jakub Kicinski <jakub.kicinski@...ronome.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Nicolas Dichtel <nicolas.dichtel@...nd.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Jiri Benc <jbenc@...hat.com>
Subject: Re: [PATCH net] netns: fix GFP flags in rtnl_net_notifyid()

On Wed, Oct 23, 2019 at 9:39 AM Guillaume Nault <gnault@...hat.com> wrote:
>
> In rtnl_net_notifyid(), we certainly can't pass a null GFP flag to
> rtnl_notify(). A GFP_KERNEL flag would be fine in most circumstances,
> but there are a few paths calling rtnl_net_notifyid() from atomic
> context or from RCU critical sections. The later also precludes the use
> of gfp_any() as it wouldn't detect the RCU case. Also, the nlmsg_new()
> call is wrong too, as it uses GFP_KERNEL unconditionally.
>
> Therefore, we need to pass the GFP flags as parameter and propagate it
> through function calls until the proper flags can be determined.
>
> In most cases, GFP_KERNEL is fine. The exceptions are:
>   * openvswitch: ovs_vport_cmd_get() and ovs_vport_cmd_dump()
>     indirectly call rtnl_net_notifyid() from RCU critical section,
>
>   * rtnetlink: rtmsg_ifinfo_build_skb() already receives GFP flags as
>     parameter.
>
> Also, in ovs_vport_cmd_build_info(), let's change the GFP flags used
> by nlmsg_new(). The function is allowed to sleep, so better make the
> flags consistent with the ones used in the following
> ovs_vport_cmd_fill_info() call.
>
> Found by code inspection.
>
> Fixes: 9a9634545c70 ("netns: notify netns id events")
> Signed-off-by: Guillaume Nault <gnault@...hat.com>

Acked-by: Pravin B Shelar <pshelar@....org>

Thanks.