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Date:   Wed, 13 Nov 2019 14:42:06 +0100
From:   Oleg Nesterov <oleg@redhat.com>
To:     Adrian Reber <areber@redhat.com>
Cc:     Christian Brauner <christian.brauner@ubuntu.com>,
        Eric Biederman <ebiederm@xmission.com>,
        Pavel Emelyanov <ovzxemul@gmail.com>,
        Jann Horn <jannh@google.com>,
        Dmitry Safonov <0x7f454c46@gmail.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        linux-kernel@vger.kernel.org, Andrei Vagin <avagin@gmail.com>,
        Mike Rapoport <rppt@linux.ibm.com>,
        Radostin Stoyanov <rstoyanov1@gmail.com>
Subject: Re: [PATCH v8 1/2] fork: extend clone3() to support setting a PID
Message-ID: <20191113134206.GA4320@redhat.com>
References: <20191113080301.1197762-1-areber@redhat.com>
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On 11/13, Adrian Reber wrote:
>
> @@ -175,23 +187,47 @@ struct pid *alloc_pid(struct pid_namespace *ns)
> =20
>  =09for (i =3D ns->level; i >=3D 0; i--) {
>  =09=09int pid_min =3D 1;

Well, this is really minor but again, pid_min is only used in the "else"
branch below, you can move this declaration there.

> +
> +=09=09if (set_tid_size) {
> +=09=09=09tid =3D set_tid[ns->level - i];
> +=09=09=09if (tid < 1 || tid >=3D pid_max)
> +=09=09=09=09return ERR_PTR(-EINVAL);
> +=09=09=09/* Also fail if a PID !=3D 1 is requested and no PID 1 exists *=
/
> +=09=09=09if (tid !=3D 1 && !tmp->child_reaper)
> +=09=09=09=09return ERR_PTR(-EINVAL);
> +=09=09=09if (!ns_capable(tmp->user_ns, CAP_SYS_ADMIN))
> +=09=09=09=09return ERR_PTR(-EPERM);
> +=09=09}
> =20
>  =09=09idr_preload(GFP_KERNEL);
>  =09=09spin_lock_irq(&pidmap_lock);
> =20
> -=09=09/*
> -=09=09 * init really needs pid 1, but after reaching the maximum
> -=09=09 * wrap back to RESERVED_PIDS
> -=09=09 */
> -=09=09if (idr_get_cursor(&tmp->idr) > RESERVED_PIDS)
> -=09=09=09pid_min =3D RESERVED_PIDS;
> -
> -=09=09/*
> -=09=09 * Store a null pointer so find_pid_ns does not find
> -=09=09 * a partially initialized PID (see below).
> -=09=09 */
> -=09=09nr =3D idr_alloc_cyclic(&tmp->idr, NULL, pid_min,
> -=09=09=09=09      pid_max, GFP_ATOMIC);
> +=09=09if (tid) {
> +=09=09=09nr =3D idr_alloc(&tmp->idr, NULL, tid,
> +=09=09=09=09       tid + 1, GFP_ATOMIC);
> +=09=09=09/*
> +=09=09=09 * If ENOSPC is returned it means that the PID is
> +=09=09=09 * alreay in use. Return EEXIST in that case.
> +=09=09=09 */
> +=09=09=09if (nr =3D=3D -ENOSPC)
> +=09=09=09=09nr =3D -EEXIST;
> +=09=09=09set_tid_size--;
                        ^^^^^^^^^^^^^^^
May I ask you to move this decrement into the "if (set_tid_size)" block abo=
ve?

Oleg.