linux-kernel - Re: How the devil can gettid() return 1?

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Date:	Mon, 8 Aug 2016 14:49:44 +0200
From:	Vegard Nossum <vegard.nossum@...il.com>
To:	Tom Horsley <horsley1953@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>
Subject: Re: How the devil can gettid() return 1?

On 8 August 2016 at 14:11, Tom Horsley <horsley1953@...il.com> wrote:
> Every once in a while google-chrome goes into a 100% cpu loop.
> I got curious and examined the thread that was running at 100%
> and strace says this over and over again till I interrupt it:
>
> gettid()                                = 1
> gettid()                                = 1
> gettid()                                = 1
> gettid()                                = 1
> ^Cstrace: Process 18863 detached
>  <detached ...>
>
> Clearly Process 18863 isn't the init process, how can it
> have a tid of 1?

If you call clone() with CLONE_NEWPID then the new process will run in
a new PID namespace (with new pids/tids starting at 1). The new
process still has a pid in the old (containing) namespace, here
presumably 18863. Chrome is probably using namespaces to isolate
itself from the rest of the system.

You can read more about CLONE_NEWPID in 'man 2 clone'.

Vegard