Re: [PATCH v3 1/2] fork: extend clone3() to support CLONE_SET_TID

[Christian Brauner]

On Tue, Aug 06, 2019 at 09:15:50PM +0200, Adrian Reber wrote:
> The main motivation to add set_tid to clone3() is CRIU.
> 
> To restore a process with the same PID/TID CRIU currently uses
> /proc/sys/kernel/ns_last_pid. It writes the desired (PID - 1) to
> ns_last_pid and then (quickly) does a clone(). This works most of the
> time, but it is racy. It is also slow as it requires multiple syscalls.
> 
> Extending clone3() to support set_tid makes it possible restore a
> process using CRIU without accessing /proc/sys/kernel/ns_last_pid and
> race free (as long as the desired PID/TID is available).
> 
> This clone3() extension places the same restrictions (CAP_SYS_ADMIN)
> on clone3() with set_tid as they are currently in place for ns_last_pid.
> 
> Signed-off-by: Adrian Reber <areber@xxxxxxxxxx>

I'm currently on vacation until 12 August so I'm going to be a little
slow in responding. Sorry about that!

Christian