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

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Date:   Wed, 27 Sep 2017 20:36:30 +0530
From:   Gargi Sharma <gs051095@...il.com>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Rik van Riel <riel@...riel.com>, linux-kernel@...r.kernel.org,
        Julia Lawall <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 Wed, Sep 27, 2017 at 7:36 PM, Oleg Nesterov <oleg@...hat.com> wrote:
> 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().
Yes, I missed this. I can simply remove the idr_get_next() before the
idr_for_each_continue and that will take care of it.

Thanks!
Gargi
>
> Oleg.
>