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Sat, 1 Feb 2025 17:46:11 +0000 (UTC) Received: by dhcp-27-174.brq.redhat.com (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Sat, 1 Feb 2025 18:45:48 +0100 (CET) Date: Sat, 1 Feb 2025 18:45:44 +0100 From: Oleg Nesterov To: Mateusz Guzik Cc: ebiederm@xmission.com, brauner@kernel.org, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 6/6] pid: drop irq disablement around pidmap_lock Message-ID: <20250201174544.GB26042@redhat.com> References: <20250201163106.28912-1-mjguzik@gmail.com> <20250201163106.28912-7-mjguzik@gmail.com> <20250201174203.GA26042@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250201174203.GA26042@redhat.com> User-Agent: Mutt/1.5.24 (2015-08-30) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 X-Rspam-User: X-Rspamd-Server: rspam01 X-Rspamd-Queue-Id: C154020007 X-Stat-Signature: denp9i16tuxz7tgjwb9jrpbwdh8dns8a X-HE-Tag: 1738431979-560927 X-HE-Meta: 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 FNB/z7SY PMZrurZu31tdKW1eWoEIt40jbb8IkqNyQEavvsN93CkR3DGLVdwG8lJduI8HgrvC1SR9DPpmpvU0FopSJOgCdicWRrwHn9B6Fy1nngUt2+bjn6cO5+Cs1wxm0cgDZEcLMjztiK91mCV6B5SW0vZiPOuvZybRtYVnqQ622spwudzaCPxzuqrOU67Etbsxv+0YkO0yUkUZTKLRlLT8uscyDAi7Dsd5EXBvSPQfMhmQJ2IsfS/G1dUogWRcqzzN3GW6rR5rmxu43w+IujRE9/Npz9M98P3VZsn8FbJV2kjYv4cJfy73fsk+F66RNLX9mRDamHXNmnqlXIhV/5q/x+QTLsf2rdQZkzVOGikrd X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 02/01, Oleg Nesterov wrote: > > However, shouldn't this patch also remove the comment which explains > the possible lock inversion? Above put_pid(), > > /* > * Note: disable interrupts while the pidmap_lock is held as an > * interrupt might come in and do read_lock(&tasklist_lock). > * > * If we don't disable interrupts there is a nasty deadlock between > * detach_pid()->free_pid() and another cpu that does > * spin_lock(&pidmap_lock) followed by an interrupt routine that does > * read_lock(&tasklist_lock); > * > * After we clean up the tasklist_lock and know there are no > * irq handlers that take it we can leave the interrupts enabled. > * For now it is easier to be safe than to prove it can't happen. > */ Ah, sorry, please forget, you did it in the previous patch. which probably needs some more discussion... Oleg.