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Sat, 14 Nov 2026 05:24:49 -0800 (PST) Received: from umang-Inspiron-3501 ([2401:4900:1c60:38c8:74f6:e2c1:4674:3e44]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-37955f01d68sm16312312eec.17.2026.11.14.05.24.45 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 14 Nov 2026 05:24:49 -0800 (PST) From: Umang Pokhriyal To: netdev-bot+sashiko@kernel.org Cc: netdev@vger.kernel.org, Willem de Bruijn , Jason Wang , Andrew Lunn , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , linux-kernel@vger.kernel.org Subject: Re: [PATCH net] tun: delete the flow entries of the moved queue on detach Date: Sat, 14 Nov 2026 18:51:50 +0530 Message-ID: <20261114132237.70664-1-umangpokhriyall@gmail.com> X-Mailer: git-send-email 2.53.0 In-Reply-To: <179415734502.994134.10139593761656069984@kernel.org> References: <20261104174240.138491-1-umangpokhriyall@gmail.com> <179415734502.994134.10139593761656069984@kernel.org> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit On Sun, 08 Nov 2026 17:02:25 +0000, netdev-bot+sashiko@kernel.org wrote: > Can a concurrent write() still put back an entry that points at the old > index after this delete has run? Yes. On the write() path tun_flow_update() reads tfile->queue_index outside any RCU section, and synchronize_net() does not wait for it. The race predates this patch. Before the patch the entries survived every detach. With it, only a write() that stalls across the synchronize_net() can store the old index again. > There are two possible fixes. One is to read tfile->queue_index and update > e->queue_index under tun->lock. The other is to have > tun_automq_select_queue() fall back to reciprocal_scale() when > e->queue_index >= numqueues. Would either of these work here? The second one covers both sequences and keeps the write() path lockless for a known flow. It would be a separate patch for net-next, since the race is old and has not been seen in practice.