netdev - Re: rtnl_lock() question

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Date:   Wed, 4 Sep 2019 09:39:07 +0200
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     Jonathan Lemon <jonathan.lemon@...il.com>,
        Netdev <netdev@...r.kernel.org>
Subject: Re: rtnl_lock() question

On 9/3/19 11:55 PM, Jonathan Lemon wrote:
> How appropriate is it to hold the rtnl_lock() across a sleepable
> memory allocation?  On one hand it's just a mutex, but it would
> seem like it could block quite a few things.
> 

Sure, all GFP_KERNEL allocations can sleep for quite a while.

On the other hand, we may want to delay stuff if memory is under pressure,
or complex operations like NEWLINK would fail.

RTNL is mostly taken for control path operations, we prefer them to be
mostly reliable, otherwise admins job would be a nightmare.

In some cases, it is relatively easy to pre-allocate memory before rtnl is taken,
but that will only take care of some selected paths.