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Tue, 15 Sep 2026 11:13:32 -0400 X-MC-Unique: exUphlHtMCWEYxi51V94Vw-1 X-Mimecast-MFC-AGG-ID: exUphlHtMCWEYxi51V94Vw_1789485210 Received: from mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.4]) (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-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 0BAB7185FCDD; Tue, 15 Sep 2026 15:13:30 +0000 (UTC) Received: from fedora (headnet03.pony-001.prod.iad2.dc.redhat.com [10.2.32.114]) by mx-prod-int-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with SMTP id 81D7A3004188; Tue, 15 Sep 2026 15:13:26 +0000 (UTC) Received: by fedora (nbSMTP-1.00) for uid 1000 oleg@redhat.com; Tue, 15 Sep 2026 17:13:29 +0200 (CEST) Date: Tue, 15 Sep 2026 17:13:25 +0200 From: Oleg Nesterov To: Christian Brauner Cc: Jens Axboe , linux-fsdevel@vger.kernel.org, Alexander Viro , Jan Kara , NeilBrown , Ingo Molnar , Peter Zijlstra , linux-mm@kvack.org, io-uring@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH 3/6] coredump: hold RCU while releasing parked threads Message-ID: References: <20260915-work-coredump-fixes-v1-0-f354ca41780c@kernel.org> <20260915-work-coredump-fixes-v1-3-f354ca41780c@kernel.org> MIME-Version: 1.0 In-Reply-To: <20260915-work-coredump-fixes-v1-3-f354ca41780c@kernel.org> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.4 X-Mimecast-MFC-PROC-ID: rZhp_sAeJBaR_rpHEcpdUhu12rnBlgFpox8AvgV3aOU_1789485210 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline X-Rspam-User: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: BBF8720006 X-Stat-Signature: dnws9mq5scopurwkjryrifuehnhrz3ed X-HE-Tag: 1789485216-817321 X-HE-Meta: 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 YnAf85Iq rDiwJClsKtfWis19ekwmy9olXQWTBbbhi9iOcP3TCaXrraBebSvL2hgBlZ45v8fUwW7Kw/dEWzuuw7KfYDP05cTKmP2GCTavSonm6H/VJ5+KkN0AfOhXIXypqJkASLsK4eAnsjbbxaTXa0zlQps+CiBKMaikKaKEekUQTCqxKusbWKagdEEWh+on42eXgIHylcnyr4n7jVMG+1jWN4xfpz2be9Iz2k88c/lzONvUcpMa8lz7l7y/IAD9YW0SOa+qxsGnjKEvEc9s297lqbyB85MZH14QZl2zOjgNhB5uM/S/1O1XGBg7RgUieIF+d7A8okDAywlJcUmFlAvFum4orgC8kWnmv5b6b/iddqpEtzF84KzLmfoxSWons19yDp2ZutFtR/Cyw+BkKMFY= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 09/15, Christian Brauner wrote: > > When coredump_finish() releases the threads the wakeup neither holds a > reference on the task nor is it inside rcu. > > The threads don't necessarily need a wakeup to exit. If it gets > preempted or was woken for other reasons it sees ->task cleared and > exits. So only rcu keeps such a task_struct alive. > > If the coredump client is preempted between the store and > wake_up_process() for longer then try_to_wake_up() takes pi_lock() in > freed memory. > > Hold the rcu across the loop. > > Fixes: a94e2d408eae ("coredump: kill mm->core_done") > Cc: stable@vger.kernel.org > Signed-off-by: Christian Brauner (Amutable) Aah, thanks... Acked-by: Oleg Nesterov But to be honest the changelog looks a bit confusing to me... curr->task = NULL; wake_up_process(task); So wake_up_process(task) is not safe, task can exit after a spurious wakeup if it sees ->task == NULL. And perhaps a short comment above "curr->task = NULL;" makes sense? The reason for guard(rcu) is not obvious at all. Oleg.