netdev - Re: [PATCH v1 net] mctp: Use __mctp_dev_get() in mctp_fill_link

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Message-ID: <20240816030818.15677-1-kuniyu@amazon.com>
Date: Thu, 15 Aug 2024 20:08:18 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <kuba@...nel.org>
CC: <davem@...emloft.net>, <edumazet@...gle.com>, <jk@...econstruct.com.au>,
	<kuni1840@...il.com>, <kuniyu@...zon.com>, <matt@...econstruct.com.au>,
	<netdev@...r.kernel.org>, <pabeni@...hat.com>
Subject: Re: [PATCH v1 net] mctp: Use __mctp_dev_get() in mctp_fill_link_af().

From: Jakub Kicinski <kuba@...nel.org>
Date: Thu, 15 Aug 2024 18:39:46 -0700
> On Thu, 15 Aug 2024 13:42:54 -0700 Kuniyuki Iwashima wrote:
> > Since commit 5fa85a09390c ("net: core: rcu-ify rtnl af_ops"),
> > af_ops->fill_link_af() is called under RCU.
> > 
> > mctp_fill_link_af() calls mctp_dev_get_rtnl() that uses
> > rtnl_dereference(), so lockdep should complain about it.
> > 
> > Let's use __mctp_dev_get() instead.
> 
> And this is what crashes kunit tests, I reckon.

Exactly, I missed that the helper increments the dev refcnt.
I'll use bare rcu_dereference().

Thanks!