Re: [PATCH] pid: restore the old behaviour of the ns_last_pid sysctl

From: Oleg Nesterov <oleg@redhat.com>
To: Andrei Vagin <avagin@openvz.org>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	linux-kernel@vger.kernel.org, Gargi Sharma <gs051095@gmail.com>
Subject: Re: [PATCH] pid: restore the old behaviour of the ns_last_pid sysctl
Date: Mon, 6 Nov 2017 15:47:33 +0100	[thread overview]
Message-ID: <20171106144733.GA19282@redhat.com> (raw)
In-Reply-To: <20171103203133.19007-1-avagin@openvz.org>

On 11/03, Andrei Vagin wrote:
>
> @@ -297,8 +298,18 @@ static int pid_ns_ctl_handler(struct ctl_table *table, int write,
>  	 * it should synchronize its usage with external means.
>  	 */
>  
> -	tmp.data = &pid_ns->idr.idr_next;
> -	return proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
> +	next = idr_get_cursor(&pid_ns->idr) - 1;
> +
> +	tmp.data = &next;
> +	ret = proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
> +	if (ret < 0)
> +		return ret;
> +
> +	if (!write)
> +		return 0;
> +
> +	idr_set_cursor(&pid_ns->idr, next + 1);
> +	return 0;

Ah yes, we should also take "write" into account, I forgot it is readable.
Can't resist, to me

	err = proc_dointvec_minmax(...);
	if (!err && write)
		idr_set_cursor(...);

	return err;

looks a bit more readable, but this is matter of taste of course.

Acked-by: Oleg Nesterov <oleg@redhat.com>