linux-kernel - Re: [v6,1/2] pid: Replace pid bitmap implementation with IDR API

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Message-ID: <20171019161800.GA8886@redhat.com>
Date:   Thu, 19 Oct 2017 18:18:00 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Andrei Vagin <avagin@...tuozzo.com>
Cc:     Gargi Sharma <gs051095@...il.com>, linux-kernel@...r.kernel.org,
        riel@...riel.com, julia.lawall@...6.fr, akpm@...ux-foundation.org,
        mingo@...nel.org, pasha.tatashin@...cle.com, ktkhai@...tuozzo.com,
        ebiederm@...ssion.com, hch@...radead.org, lkp@...el.com,
        tony.luck@...el.com
Subject: Re: [v6,1/2] pid: Replace pid bitmap implementation with IDR API

On 10/19, Andrei Vagin wrote:
>
> Hi Gargi,
>
> This patch breaks CRIU, because it changes a meaning of ns_last_pid.

...

> > @@ -311,7 +297,7 @@ static int pid_ns_ctl_handler(struct ctl_table *table, int write,
> >  	 * it should synchronize its usage with external means.
> >  	 */
> >  
> > -	tmp.data = &pid_ns->last_pid;
> > +	tmp.data = &pid_ns->idr.idr_next;

Ah, yes, off-by-one error...

Gargi, I don't think you need to make another version, I'd suggest you to send
the trivial fix to Andrew, afaics you just need to replace these 2 lines with

	unsigned int last;
	int err;

	tmp.data = &last;
	err = proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
	if (!err)
		idr_set_cursor(&pid_ns->idr, last + 1);
	return err;

Oleg.