Re: [PATCH 1/3] pid: Remove the child_reaper special case in init/main.c

["Serge E. Hallyn" <serge.hallyn@canonical.com>]

Quoting Daniel Lezcano (daniel.lezcano@free.fr):
> From: Eric W. Biederman <ebiederm@xmission.com>
> 
> It turns out that the existing assignment in copy_process of
> the child_reaper can handle the initial assignment of child_reaper
> we just need to generalize the test in kernel/fork.c
> 
> Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
> Signed-off-by: Daniel Lezcano <daniel.lezcano@free.fr>

Acked-by: Serge E. Hallyn <serge@hallyn.com>

> ---
>  include/linux/pid.h |   11 +++++++++++
>  init/main.c         |    9 ---------
>  kernel/fork.c       |    2 +-
>  3 files changed, 12 insertions(+), 10 deletions(-)
> 
> diff --git a/include/linux/pid.h b/include/linux/pid.h
> index 49f1c2f..efceda0 100644
> --- a/include/linux/pid.h
> +++ b/include/linux/pid.h
> @@ -141,6 +141,17 @@ static inline struct pid_namespace *ns_of_pid(struct pid *pid)
>  }
>  
>  /*
> + * is_child_reaper returns true if the pid is the init process
> + * of the current namespace. As this one could be checked before
> + * pid_ns->child_reaper is assigned in copy_process, we check
> + * with the pid number.
> + */
> +static inline bool is_child_reaper(struct pid *pid)
> +{
> +	return pid->numbers[pid->level].nr == 1;
> +}
> +
> +/*
>   * the helpers to get the pid's id seen from different namespaces
>   *
>   * pid_nr()    : global id, i.e. the id seen from the init namespace;
> diff --git a/init/main.c b/init/main.c
> index 33c37c3..793ebfd 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -875,15 +875,6 @@ static int __init kernel_init(void * unused)
>  	 * init can run on any cpu.
>  	 */
>  	set_cpus_allowed_ptr(current, cpu_all_mask);
> -	/*
> -	 * Tell the world that we're going to be the grim
> -	 * reaper of innocent orphaned children.
> -	 *
> -	 * We don't want people to have to make incorrect
> -	 * assumptions about where in the task array this
> -	 * can be found.
> -	 */
> -	init_pid_ns.child_reaper = current;
>  
>  	cad_pid = task_pid(current);
>  
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 25e4291..c9f0784 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1289,7 +1289,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
>  		tracehook_finish_clone(p, clone_flags, trace);
>  
>  		if (thread_group_leader(p)) {
> -			if (clone_flags & CLONE_NEWPID)
> +			if (is_child_reaper(pid))
>  				p->nsproxy->pid_ns->child_reaper = p;
>  
>  			p->signal->leader_pid = pid;
> -- 
> 1.7.1
> 
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