How the devil can gettid() return 1?

How the devil can gettid() return 1?

[Tom Horsley]

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?

This is on a fedora 24 box with a 4.6 kernel:

Linux tomh 4.6.4-301.fc24.x86_64 #1 SMP Tue Jul 12 11:50:00 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

Just curious...

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

[Vegard Nossum]

On 8 August 2016 at 14:11, Tom Horsley <horsley1953@gmail.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