netdev - Re: [PATCH net-next v3] net: add rcu annotations for ifa

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Message-Id: <20190602.181107.2095462509842063351.davem@davemloft.net>
Date:   Sun, 02 Jun 2019 18:11:07 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     fw@...len.de
Cc:     netdev@...r.kernel.org
Subject: Re: [PATCH net-next v3] net: add rcu annotations for ifa_list

From: Florian Westphal <fw@...len.de>
Date: Fri, 31 May 2019 18:27:02 +0200

> v3: fix typo in patch1 commit message
>     All other patches are unchanged.
> v2: remove ifa_list iteration in afs instead of conversion
> 
> Eric Dumazet reported following problem:
> 
>   It looks that unless RTNL is held, accessing ifa_list needs proper RCU
>   protection.  indev->ifa_list can be changed under us by another cpu
>   (which owns RTNL) [..]
> 
>   A proper rcu_dereference() with an happy sparse support would require
>   adding __rcu attribute.
> 
> This patch series does that: add __rcu to the ifa_list pointers.
> That makes sparse complain, so the series also adds the required
> rcu_assign_pointer/dereference helpers where needed.
> 
> All patches except the last one are preparation work.
> Two new macros are introduced for in_ifaddr walks.
> 
> Last patch adds the __rcu annotations and the assign_pointer/dereference
> helper calls.
> 
> This patch is a bit large, but I found no better way -- other
> approaches (annotate-first or add helpers-first) all result in
> mid-series sparse warnings.
> 
> This series is submitted vs. net-next rather than net for several
> reasons:
> 
> 1. Its (mostly) compile-tested only
> 2. 3rd patch changes behaviour wrt. secondary addresses
>    (see changelog)
> 3. The problem exists for a very long time (2004), so it doesn't
>    seem to be urgent to fix this -- rcu use to free ifa_list
>    predates the git era.

Series applied, thanks Florian.