Re: [PATCH net-next] devlink: Make devlink_register to be void

From: Leon Romanovsky <leon@kernel.org>
To: Jakub Kicinski <kuba@kernel.org>
Cc: "David S . Miller" <davem@davemloft.net>,
	Alexandre Belloni <alexandre.belloni@bootlin.com>,
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	Coiby Xu <coiby.xu@gmail.com>,
	Derek Chickles <dchickles@marvell.com>,
	drivers@pensando.io, Felix Manlunas <fmanlunas@marvell.com>,
	Florian Fainelli <f.fainelli@gmail.com>,
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	Vladimir Oltean <vladimir.oltean@nxp.com>,
	Yisen Zhuang <yisen.zhuang@huawei.com>
Subject: Re: [PATCH net-next] devlink: Make devlink_register to be void
Date: Tue, 21 Sep 2021 05:19:06 +0300	[thread overview]
Message-ID: <YUlBGk2Mq3iYhtku@unreal> (raw)
In-Reply-To: <20210920140407.0732b3d0@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>

On Mon, Sep 20, 2021 at 02:04:07PM -0700, Jakub Kicinski wrote:
> On Mon, 20 Sep 2021 13:39:15 -0700 Jakub Kicinski wrote:
> > On Mon, 20 Sep 2021 17:41:44 +0300 Leon Romanovsky wrote:
> > > From: Leon Romanovsky <leonro@nvidia.com>
> > > 
> > > devlink_register() can't fail and always returns success, but all drivers
> > > are obligated to check returned status anyway. This adds a lot of boilerplate
> > > code to handle impossible flow.
> > > 
> > > Make devlink_register() void and simplify the drivers that use that
> > > API call.  
> > 
> > Unlike unused functions bringing back error handling may be
> > non-trivial. I'd rather you deferred such cleanups until you're 
> > ready to post your full rework and therefore give us some confidence 
> > the revert will not be needed.
> 
> If you disagree you gotta repost, new devlink_register call got added
> in the meantime.

This is exactly what I afraid, new devlink API users are added faster
than I can cleanup them.

For example, let's take a look on newly added ipc_devlink_init(), it is
called conditionally "if (stage == IPC_MEM_EXEC_STAGE_BOOT) {". How can
it be different stage if we are in driver .probe() routine?

They also introduced devlink_sio.devlink_read_pend and
devlink_sio.read_sem to protect from something that right position of
devlink_register() will fix. I also have serious doubts that their
current protection is correct, once they called to devlink_params_publish()
the user can crash the system, because he can access the parameters before
they initialized their protection.

So yes, I disagree. We will need to make sure that devlink_register()
can't fail and it will make life easier for everyone (no need to unwind)
while we put that command  being last in probe sequence.

If I repost, will you take it? I don't want to waste anyone time if it
is not.

Thanks