netdev - Re: [iproute PATCH] lib/namespace: avoid double-mounting a /sys

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Message-ID: <20180727134505.4065994f@xeon-e3>
Date:   Fri, 27 Jul 2018 13:45:05 -0700
From:   Stephen Hemminger <stephen@...workplumber.org>
To:     Lubomir Rintel <lkundrak@...sk>
Cc:     netdev@...r.kernel.org, Phil Sutter <phil@....cc>
Subject: Re: [iproute PATCH] lib/namespace: avoid double-mounting a /sys

On Tue, 24 Jul 2018 19:26:38 +0200
Lubomir Rintel <lkundrak@...sk> wrote:

> This partly reverts 8f0807023d067e2bb585a2ae8da93e59689d10f1, bringing
> back the umount(/sys) attempt.
> 
> In a LXC container we're unable to umount the sysfs instance, nor mount
> a read-write one. We still are able to create a new read-only instance.
> 
> Nevertheless, it still makes sense to attempt the umount() even though
> the sysfs is mounted read-only. Otherwise we may end up attempting to
> mount a sysfs with the same flags as is already mounted, resulting in
> an EBUSY error (meaning "Already mounted").
> 
> Perhaps this is not a very likely scenario in real world, but we hit
> it in NetworkManager test suite and makes netns_switch() somewhat more
> robust. It also fixes the case, when /sys wasn't mounted at all.
> 
> Signed-off-by: Lubomir Rintel <lkundrak@...sk>

Makes sens applied.