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Date: Tue, 03 May 2022 00:49:16 +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 00:31, 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.



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