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Thu, 26 Feb 2026 11:07:30 -0500 X-MC-Unique: R2Ypp91zP6S3qLZxgWU9VQ-1 X-Mimecast-MFC-AGG-ID: R2Ypp91zP6S3qLZxgWU9VQ_1772122046 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id E26A01956089; Thu, 26 Feb 2026 16:07:25 +0000 (UTC) Received: from fedora (unknown [10.44.32.38]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id E5E5B1800465; Thu, 26 Feb 2026 16:07:18 +0000 (UTC) Received: by fedora (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Thu, 26 Feb 2026 17:07:25 +0100 (CET) Date: Thu, 26 Feb 2026 17:07:17 +0100 From: Oleg Nesterov To: Andrei Vagin Cc: Pavel Tikhomirov , Christian Brauner , Shuah Khan , Kees Cook , Andrew Morton , David Hildenbrand , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Jan Kara , Aleksa Sarai , Andrei Vagin , Kirill Tkhai , Alexander Mikhalitsyn , Adrian Reber , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-kselftest@vger.kernel.org Subject: Re: [PATCH v3 2/4] pid: check init is created first after idr alloc Message-ID: References: <20260224164852.306583-1-ptikhomirov@virtuozzo.com> <20260224164852.306583-3-ptikhomirov@virtuozzo.com> MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 X-Mimecast-MFC-PROC-ID: 4Iksx0osVbqVpSrLAFITRqyz_2jHiwquVuUtFJ1-vuQ_1772122046 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Rspamd-Queue-Id: 63415180012 X-Stat-Signature: ifetpzc4bawackgdkqpcmteby5k6d959 X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1772122054-487981 X-HE-Meta: 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 NC2WyL4s 0WEXKKdMELK7VfESKjm/+SgZTD5puCP+Be5S2rCGxfirDyLpwdLFKkgmJTkaZ0NbS5xnOR+hTyRgKlgMXJ+Dd80f/shF45p56TCYK7cKq1gd6IT3bANFAc7wBpmISoOmGhJDaqOmNToBPisyFhVV1Aoe9MdBKZmA3oc0xazPDQr4AkIqNs6n7z3v+X3TU6GrSU2K5dqk/2uTO/R4/pmHxEk6jbUdqCHfaphwy4ZPOjgUxbcoJ+rUEB2ArG3bFC7g3zj9/p6kV60HSWxpwi1JKDyDNZgakGpmRQ7cda81TVxUeU0dcY4OkRJcwa8ccCktVttu/ Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 02/26, Oleg Nesterov wrote: > > On 02/26, Oleg Nesterov wrote: > > > > Now that I look at this code again... Why do we bother to check > > "pid_allocated & PIDNS_ADDING" at all? copy_process() does > > > > /* Don't start children in a dying pid namespace */ > > if (unlikely(!(ns_of_pid(pid)->pid_allocated & PIDNS_ADDING))) { > > retval = -ENOMEM; > > goto bad_fork_core_free; > > } > > > > I am going to send the patch which removes this check from alloc_pid... > > Need to recheck. > > No, we can't remove either of these 2 checks... > > This probably deserves another comment in alloc_pid(). something like We need this even if copy_process() does the same check. If two or more tasks from parent namespace try to inject a child into a dead namespace, one of free_pid() calls from the copy_process() error path may try to wakeup the possibly freed ns->child_reaper. perhaps? does it look clear enough? Oleg.