linux-kernel - Re: [PATCH] netdevsim: remove incorrect __net

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Date:   Wed, 04 Apr 2018 12:54:08 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     arnd@...db.de
Cc:     jakub.kicinski@...ronome.com, dsa@...ulusnetworks.com,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] netdevsim: remove incorrect __net_initdata annotations

From: Arnd Bergmann <arnd@...db.de>
Date: Wed, 4 Apr 2018 18:03:41 +0200

> On Wed, Apr 4, 2018 at 5:52 PM, David Miller <davem@...emloft.net> wrote:
>> From: Arnd Bergmann <arnd@...db.de>
>> Date: Wed,  4 Apr 2018 14:12:39 +0200
>>
>>> The __net_initdata section cannot currently be used for structures that
>>> get cleaned up in an exitcall using unregister_pernet_operations:
>>>
>>> WARNING: vmlinux.o(.text+0x868c34): Section mismatch in reference from the function nsim_devlink_exit() to the (unknown reference) .init.data:(unknown)
>>> The function nsim_devlink_exit() references
>>> the (unknown reference) __initdata (unknown).
>>> This is often because nsim_devlink_exit lacks a __initdata
>>> annotation or the annotation of (unknown) is wrong.
>>> WARNING: vmlinux.o(.text+0x868c64): Section mismatch in reference from the function nsim_devlink_init() to the (unknown reference) .init.data:(unknown)
>>> WARNING: vmlinux.o(.text+0x8692bc): Section mismatch in reference from the function nsim_fib_exit() to the (unknown reference) .init.data:(unknown)
>>> WARNING: vmlinux.o(.text+0x869300): Section mismatch in reference from the function nsim_fib_init() to the (unknown reference) .init.data:(unknown)
>>>
>>> As that warning tells us, discarding the structure after a module is
>>> loaded would lead to a undefined behavior when that module is removed.
>>>
>>> It might be possible to change that annotation so it has no effect for
>>> loadable modules, but I have not figured out exactly how to do that, and
>>> we want this to be fixed in -rc1.
>>>
>>> This just removes the annotations, just like we do for all other such
>>> modules.
>>>
>>> Fixes: 37923ed6b8ce ("netdevsim: Add simple FIB resource controller via devlink")
>>> Signed-off-by: Arnd Bergmann <arnd@...db.de>
>>
>> Hmmm...
>>
>> __net_initdata defines to nothing if network namespaces are enabled.
>>
>> That's the whole point.
>>
>> Therefore, if NETNS is disabled, "unregister_pernet_operations" cannot
>> happen and this is the only time when __net_initdata actually does
>> something.
> 
> The problem happens with CONFIG_NETNS=n: __net_initdata turns into
> __initdata, and nsim_fib_net_ops is referenced from a function that is
> not marked __init (i.e. nsim_fib_exit).
> 
> The logic to turn __net_initdata into __init only makes sense for
> subsystems that have no way to be unregistered, i.e. code which is
> always built-in, or non-unloadable modules.

Ok, I see it.

I'll apply this for now, thanks.