netdev - Re: [PATCH] netdevsim: remove incorrect __net

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Date:   Wed, 04 Apr 2018 11:52:15 -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 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.