linux-kernel - Re: [PATCH v2 1/2] pid: Replace pid bitmap implementation with IDR API

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Date:   Wed, 27 Sep 2017 16:06:58 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Rik van Riel <riel@...riel.com>
Cc:     Gargi Sharma <gs051095@...il.com>, linux-kernel@...r.kernel.org,
        julia.lawall@...6.fr, akpm@...ux-foundation.org, mingo@...nel.org,
        pasha.tatashin@...cle.com, ktkhai@...tuozzo.com
Subject: Re: [PATCH v2 1/2] pid: Replace pid bitmap implementation with IDR
 API

On 09/27, Rik van Riel wrote:
>
> > @@ -240,17 +230,18 @@ void zap_pid_ns_processes(struct pid_namespace
> > *pid_ns)
> >  	 *
> >  	 */
> >  	read_lock(&tasklist_lock);
> > -	nr = next_pidmap(pid_ns, 1);
> > -	while (nr > 0) {
> > -		rcu_read_lock();
> > +	pid = idr_get_next(&pid_ns->idr, &nr);
> > +	while (pid) {
> >  
> > -		task = pid_task(find_vpid(nr), PIDTYPE_PID);
> > -		if (task && !__fatal_signal_pending(task))
> > -			send_sig_info(SIGKILL, SEND_SIG_FORCED,
> > task);
> > +		rcu_read_lock();
> >  
> > +		idr_for_each_entry_continue(&pid_ns->idr, pid, nr) {
> > +			task = pid_task(pid, PIDTYPE_PID);
> > +			if (task && !__fatal_signal_pending(task))
> > +				send_sig_info(SIGKILL,
> > SEND_SIG_FORCED, task);
> > +		}
> >  		rcu_read_unlock();
> >  
> > -		nr = next_pidmap(pid_ns, nr);
> >  	}
> >  	read_unlock(&tasklist_lock);
> >  
> 
> I believe we should be fine with just the idr_for_each_entry_continue()
> surrounding the loop,

Yes, and please move "nr = 2" close to idr_for_each_entry_continue() to
make it clear why do we use _continue (to skip nr == 1).

> and not need the while (pid) around that.
>
> That should still iterate over all the pids in the namespace, and
> simplify the code even more.

And make this patch correct ;)

because currently it is wrong, zap_pid_ns_processes() won't kill the pid
returned by the first idr_get_next().

Oleg.