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Date: Mon, 2 May 2022 17:31:53 -0400
From: Carlos O'Donell <>
To:, Florian Weimer <>,
 Rich Felker <>
Cc: Alexey Izbyshev <>
Subject: Re: vfork()-based posix_spawn() has more failure modes than
 fork()-based one

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?


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