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Wed, 25 Feb 2026 10:46:48 -0800 (PST) MIME-Version: 1.0 References: <20260225133229.550302-1-ptikhomirov@virtuozzo.com> <20260225133229.550302-3-ptikhomirov@virtuozzo.com> In-Reply-To: <20260225133229.550302-3-ptikhomirov@virtuozzo.com> From: Andrei Vagin Date: Wed, 25 Feb 2026 10:46:35 -0800 X-Gm-Features: AaiRm50yP7U5Mblj8nExlDPbtbQY6Smjt4Ct49GvH3x6Zklgi4smtXG6r6gKV_U Message-ID: Subject: Re: [PATCH v4 2/4] pid: check init is created first after idr alloc To: Pavel Tikhomirov Cc: Christian Brauner , Shuah Khan , Kees Cook , Andrew Morton , David Hildenbrand , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Jan Kara , Oleg Nesterov , Aleksa Sarai , Kirill Tkhai , Alexander Mikhalitsyn , Adrian Reber , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: ucu6m4g5tig3ijru6imhkz71wp1x3r3f X-Rspamd-Server: rspam11 X-Rspam-User: X-Rspamd-Queue-Id: A311C40006 X-HE-Tag: 1772045209-563598 X-HE-Meta: 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Feb 25, 2026 at 5:33=E2=80=AFAM Pavel Tikhomirov wrote: > > This moves the condition (tid !=3D 1 && !tmp->child_reaper) to after idr > alloc, so it not only covers that first process in pid namespace has pid > 1 in case of clone3(set_tid) requesting wrong pid, but also if idr > itself gives wrong pid for some reason. > > This could've been the case before this patch, when creating first > process the alloc_pid()->pidfs_add_pid() code path fails, so that the > idr->idr_next is non zero anymore and next process calling to > alloc_pid(), will get 2 as a pid from idr_alloc_cyclic(). Though thanks > to PIDNS_ADDING logic, free_pid() disables further pid allocation in > this case and it does not lead to any real problem. > > Note: This is also a preparation for the next patch in the series, which > will introduce an ability of creating init from the task different to > the task which had created the pid namespace. Needed to make sure that > init is always first, even in this new case. > > Suggested-by: Oleg Nesterov > Signed-off-by: Oleg Nesterov > Signed-off-by: Pavel Tikhomirov Acked-by: Andrei Vagin Thanks, Andrei