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Date: Tue, 03 May 2022 00:56:24 +0300
From: Alexey Izbyshev <>
Cc: Florian Weimer <>, Rich Felker <>,
 Andrei Vagin <>, Christian Brauner <>
Subject: Re: vfork()-based posix_spawn() has more failure modes than
 fork()-based one

On 2022-05-03 00:49, Alexey Izbyshev wrote:
> On 2022-05-03 00:31, Carlos O'Donell wrote:
>> On 5/2/22 17:25, Florian Weimer wrote:
>>> * Rich Felker:
>>>> I'm trying to understand how this comes to be. The child should
>>>> inherit the namespaces of the parent and thus should not be in a
>>>> different namespace that precludes spawn. I'm guessing this is some
>>>> oddity where unshare doesn't affect the process itself, only its
>>>> children? If so, it seems like a bug that it doesn't affect the
>>>> process itself after execve (after unshare(1) runs your test 
>>>> program),
>>>> but that probably can't be fixed now on the Linux side for stability
>>>> reasons. :(
>>> It's about fundamentally conflicting requirements.
>>> The vDSO data mapping needs to store the time offset, so it has to be
>>> distinct from the original namespace.  vfork preserves the VM 
>>> sharing.
>>> It's not possible to do both things at the same time.
>>> unshare(CLONE_NEWTIME) should have been specified to only take effect
>>> after execve, when the vDSO is remapped anyway.
>> Can we ask some kernel developers for an opinion?
> Christian Brauner had some comments [1,2] on this. Time namespaces
> were added in [3] by Andrei Vagin. Adding both to CC.
(Trying a different email for Andrei Vagin)

> Alexey
> [1]
> [2]
> [3] 

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