netdev - Re: [PATCH net-next v13 2/4] ethtool: provide customized dim profile management

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Date: Mon, 13 May 2024 22:52:13 +0800
From: Heng Qi <hengqi@...ux.alibaba.com>
To: Jakub Kicinski <kuba@...nel.org>
Cc: kernel test robot <lkp@...el.com>,
 llvm@...ts.linux.dev,
 oe-kbuild-all@...ts.linux.dev,
 "David S . Miller" <davem@...emloft.net>,
 Paolo Abeni <pabeni@...hat.com>,
 Eric Dumazet <edumazet@...gle.com>,
 Jason  Wang <jasowang@...hat.com>,
 "Michael S . Tsirkin" <mst@...hat.com>,
 Brett  Creeley <bcreeley@....com>,
 Ratheesh Kannoth <rkannoth@...vell.com>,
 Alexander Lobakin <aleksander.lobakin@...el.com>,
 Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
 Tal Gilboa <talgi@...dia.com>,
 Jonathan  Corbet <corbet@....net>,
 linux-doc@...r.kernel.org,
 Maxime Chevallier <maxime.chevallier@...tlin.com>,
 Jiri Pirko <jiri@...nulli.us>,
 Paul  Greenwalt <paul.greenwalt@...el.com>,
 Ahmed Zaki <ahmed.zaki@...el.com>,
 Vladimir Oltean <vladimir.oltean@....com>,
 Kory Maincent <kory.maincent@...tlin.com>,
 Andrew Lunn <andrew@...n.ch>,
 justinstitt@...gle.com,
 donald.hunter@...il.com,
 netdev@...r.kernel.org,
 virtualization@...ts.linux.dev
Subject: Re: [PATCH net-next v13 2/4] ethtool: provide customized dim profile management

On Mon, 13 May 2024 07:22:49 -0700, Jakub Kicinski <kuba@...nel.org> wrote:
> On Mon, 13 May 2024 00:36:58 +0800 Heng Qi wrote:
> > This failed use case seems to come from this series triggering a problem that
> > has not been triggered historically, namely lockdep_rtnl_is_held() is not called
> > in an environment where CONFIG_NET is not configured and CONFIG_PROVE_LOCKING is
> > configured:
> >   If CONFIG_PROVE_LOCKING is configured as Y and CONFIG_NET is n, then
> >   lockdep_rtnl_is_held is in an undefined state at this time.
> > 
> > So I think we should declare "CONFIG_PROVE_LOCKING depends on CONFIG_NET".
> > How do you think?
> 
> Doesn't sound right, `can we instead make building lib/dim/net_dim.c

Why? IIUC, the reason is that if CONFIG_NET is not set to Y, the net/core
directory will not be compiled, so the lockdep_rtnl_is_held symbol is not
present.

> dependent on CONFIG_NET? Untested but I'm thinking something like:
> 
> diff --git a/lib/dim/Makefile b/lib/dim/Makefile
> index c4cc4026c451..c02c306e2975 100644
> --- a/lib/dim/Makefile
> +++ b/lib/dim/Makefile
> @@ -4,4 +4,8 @@
>  
>  obj-$(CONFIG_DIMLIB) += dimlib.o
>  
> -dimlib-objs := dim.o net_dim.o rdma_dim.o
> +dimlib-objs := dim.o rdma_dim.o
> +
> +ifeq ($(CONFIG_NET),y)
> +dimlib-objs += net_dim.o
> +endif

1. This is unlikely to work if the kernel is configured as[1]:

[1] kernel configuration
CONFIG_NET=n, CONFIG_ETHTOOL_NETLINK=n, CONFIG_PROVE_LOCKING=y,
(CONFIG_FSL_MC_DPIO=y && CONFIG_FSL_MC_BUS=y) select CONFIG_DIMLIB=y.

Then, because CONFIG_NET is not enabled, so there is no net_dim.o,
the following warning appears:

ld.lld: error: undefined symbol: net_dim_get_rx_moderation
referenced by dpio-service.c
drivers/soc/fsl/dpio/dpio-service.o:(dpaa2_io_dim_work) in archive vmlinux.a

ld.lld: error: undefined symbol: net_dim
referenced by dpio-service.c
drivers/soc/fsl/dpio/dpio-service.o:(dpaa2_io_update_net_dim) in archive vmlinux.a

2. If we declare "CONFIG_DIMLIB depends on CONFIG_NET",
if the configuration is still [1]:
Then the result is:
CONFIG_DIMLIB=Y (selected by CONFIG_FSL_MC_DPIO=y && CONFIG_FSL_MC_BUS=y),
CONFIG_NET=n, but we declared "CONFIG_DIMLIB depends on CONFIG_NET",
there is still a compilation error because the lockdep_rtnl_is_held symbol
cannot be found.

3. If we declare "CONFIG_DIMLIB select CONFIG_NET" and kernel configuration is [1],
then a circular dependency warning will appear:

CONFIG_DIMLIB select CONFIG_NET, ETHTOOL_NETLINK=Y(depends on CONFIG_NET)
selects CONFIG_DIMLIB. CONFIG_DIMLIB will select CONFIG_NET...

> 
>