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Date:   Tue, 24 Jan 2017 18:01:53 +0300
From:   Pavel Tikhomirov <ptikhomirov@...tuozzo.com>
To:     Oleg Nesterov <oleg@...hat.com>
CC:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Nicolas Pitre <nicolas.pitre@...aro.org>,
        Michal Hocko <mhocko@...e.com>,
        Stanislav Kinsburskiy <skinsbursky@...tuozzo.com>,
        Mateusz Guzik <mguzik@...hat.com>,
        <linux-kernel@...r.kernel.org>,
        Pavel Emelyanov <xemul@...tuozzo.com>,
        Konstantin Khorenko <khorenko@...tuozzo.com>
Subject: Re: [PATCH] introduce the walk_process_tree() helper


Will include it in patch-set with documentation fix. Thanks Oleg!

Reviewed-by: Pavel Tikhomirov <ptikhomirov@...tuozzo.com>

On 01/23/2017 02:57 PM, Oleg Nesterov wrote:
> Add the new helper to walk the process tree, the next patch adds a user.
> Note that it visits the group leaders only, proc_visitor can do
> for_each_thread itself or we can trivially extend walk_process_tree() to
> do this.
>
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  include/linux/sched.h |  3 +++
>  kernel/fork.c         | 32 ++++++++++++++++++++++++++++++++
>  2 files changed, 35 insertions(+)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index e9c009d..681f748 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -3015,6 +3015,9 @@ extern bool current_is_single_threaded(void);
>  #define for_each_process_thread(p, t)	\
>  	for_each_process(p) for_each_thread(p, t)
>
> +typedef int (*proc_visitor)(struct task_struct *p, void *data);
> +void walk_process_tree(struct task_struct *top, proc_visitor, void *);
> +
>  static inline int get_nr_threads(struct task_struct *tsk)
>  {
>  	return tsk->signal->nr_threads;
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 663c6a7..2522bae 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -2042,6 +2042,38 @@ SYSCALL_DEFINE5(clone, unsigned long, clone_flags, unsigned long, newsp,
>  }
>  #endif
>
> +void walk_process_tree(struct task_struct *top, proc_visitor visitor, void *data)
> +{
> +	struct task_struct *leader, *parent, *child;
> +	int res;
> +
> +	read_lock(&tasklist_lock);
> +	leader = top = top->group_leader;
> +down:
> +	for_each_thread(leader, parent) {
> +		list_for_each_entry(child, &parent->children, sibling) {
> +			res = visitor(child, data);
> +			if (res) {
> +				if (res < 0)
> +					goto out;
> +				leader = child;
> +				goto down;
> +			}
> +up:
> +			;
> +		}
> +	}
> +
> +	if (leader != top) {
> +		child = leader;
> +		parent = child->real_parent;
> +		leader = parent->group_leader;
> +		goto up;
> +	}
> +out:
> +	read_unlock(&tasklist_lock);
> +}
> +
>  #ifndef ARCH_MIN_MMSTRUCT_ALIGN
>  #define ARCH_MIN_MMSTRUCT_ALIGN 0
>  #endif
>

-- 
Best regards, Tikhomirov Pavel
Software Developer, Virtuozzo.

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