From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pl1-f179.google.com (mail-pl1-f179.google.com [209.85.214.179]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 2CE643F7877 for ; Wed, 3 Jun 2026 18:39:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.214.179 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780511962; cv=none; b=QZZWET59Q2vtnu8Pugvpf9xCiyYCxn+RTADjb9wpmaC8Lxl+tQ/XyKvwC0voLlV5lFdPLAqt6zM/gm6ib5Mxzej2dMzhRTE7eMHhSdmozVCa/9v1r+o5eiQ+FGwf72x00MKxC6eB0NT0bkjabcrD/Xv3CF3cL+L1P9hBMzVDVWs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1780511962; c=relaxed/simple; bh=/d5vu6FzDjUdc5vpSBDYQ8aC7S33EdRfCZpNFO9YxIQ=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=WhGmTKigWEO/+gjFBukjRJCuYRCVUvyO30BI7pUDPRYo2Y/0A/DygPZJuw2zn6GBojAleJ6O+wm3lAQgkLb2SX3wdG6rj3kSjaXNPn1vld6z9pZUFhXCdG42VOvsP1f0ADFeGvqfCuoatosSIamX2Y3bV2B6eYrAp198qgAJPn8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=f5xcVt3N; arc=none smtp.client-ip=209.85.214.179 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="f5xcVt3N" Received: by mail-pl1-f179.google.com with SMTP id d9443c01a7336-2bf2e8ccca1so35408115ad.0 for ; Wed, 03 Jun 2026 11:39:17 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20251104; t=1780511957; x=1781116757; darn=lists.linux.dev; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:from:to:cc:subject:date :message-id:reply-to; bh=79BiaAS61yq6Rc+Pw8/ABQwHPoIuPnEBPhTKKYRqkTY=; b=f5xcVt3N8J14s3fsHwy0fxKQinuY+bvgNTU1UIUpCjHP1uRGqn0SsVoZEeUe/EonOV v+HcNM2Ods1dVXic+/pzR/vI6htUXtbCApJ+L4lJtnqQlWaKmBRhugqLJuUX7wh4I8YH mLGAahuzOMjAaVe5d/t38Boqp98N0ty7dWnzHocRovg6EdvuSie0Ex5LDS5XdtOSZV4o 78ya8IA8dPLLVoqxJvXcCbJ4S9HnCIldSyEwbsbvBdaWe57YW/GqsNraf7VzNqpmSWMM tmb/AyZdEuhMEx09LCJdXDLH9fZniuFrYJzHGRlrJpdXgQ3tOKLTDQaxYfu+WeXGOVU+ ajHw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1780511957; x=1781116757; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:date:subject:cc:to:from:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=79BiaAS61yq6Rc+Pw8/ABQwHPoIuPnEBPhTKKYRqkTY=; b=hBXYMAMmZYRjId5JER64KyAcN+w5vkQ/GrSV2HJ9V76731VwDmCkho2OxJlLSdeRnJ OOxCw1S1+UsV9PczBasMlv5TpjUYmpLxRQcK88JfuGwQdjKyw5yko9Q220AOfRdgLjGt IGB6LpPCeQWeM1Dsi/QyHz4hsZ0RXtSfbpLI1xYKpVT5UNvZJdAuy486kg2xut3TIDjO ZNbPOx4SKBWuUOOzT42Czlf2wImQOKN+jWfdZnikQJjNdVlkCCLiIqyweTLQofowFZH+ 2vqY3+8MBUiDpFslHAAXr9aOKeBmM+C2m0eTN+xxgVoBAVbyCCtwVvQP/Id/S8ABzzZV FP6Q== X-Gm-Message-State: AOJu0YxsbFXIjm9OU7mi5HMcr7dMHhk3FDFp7o555ZUVOKoGxpFMuHTo ffjiLoSCtHlLlFwwe6aWioiGahtuv7NlUBskZCKWQ5SSNCA2RYsPw+Nn X-Gm-Gg: Acq92OFi4Qg4G54Mi7XKMjYxwAq8ItmxlmNn0NyBpCmquUGa0dG09Gkl54CPd8gjWat gRMNFw7ZvAc4Q8WE3qNudNSEArCZ50X+oHFjIR1JWid3c5x2nO0MHtP5AIK/oZp061DHm76rB+A ns2vhS2dncBiFmkok2NoyUvRryMh+NSQkBYb2Mf83BNlG2RaQnmKe7J7EBARmONHq7KAaNKHCME 2poXqi5ZVIBvXVzNfY+fnednGzQxhZX4Mtoe4F7qF/ENQRH6y/H2gY07IzBtJb/zzt0NYluhYlI T9WHbA38ez38qi4uiTnqa1s0P69uNjg2oNfDrXUXkz47XmZmt0kGwBrqvN6UrxcbJgyUce9PpcT QvwmoQhg+Z6ZJusmYGD6Hr4sIWnRlWB0WGpwjI97bsRt3UWSZpG8JgZGegdMZ6r4jc18ETVhBAZ l2AaeEVjWYrZEHqGz972az5iLcDjD9KbjZF8O9p69j/vFs6RdqIRTJViHTE8AzB24EGJySNalWV uJqnfgxvCjWcnyh5Sry8KM2ZzQLDQ6+7kSDkg== X-Received: by 2002:a17:903:4b50:b0:2c0:a373:89b9 with SMTP id d9443c01a7336-2c163a24bf2mr49279105ad.6.1780511957045; Wed, 03 Jun 2026 11:39:17 -0700 (PDT) Received: from baver-zenith.localdomain ([124.49.88.131]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-2c16649c01asm32764915ad.74.2026.06.03.11.39.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 03 Jun 2026 11:39:16 -0700 (PDT) From: Sungho Bae To: amit@kernel.org, arnd@arndb.de, gregkh@linuxfoundation.org Cc: virtualization@lists.linux.dev, linux-kernel@vger.kernel.org, Sungho Bae Subject: [PATCH v3 2/4] virtio_console: fix hot-unplug races in TX paths Date: Thu, 4 Jun 2026 03:37:55 +0900 Message-Id: <20260603183757.21587-3-baver.bae@gmail.com> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20260603183757.21587-1-baver.bae@gmail.com> References: <20260603183757.21587-1-baver.bae@gmail.com> Precedence: bulk X-Mailing-List: virtualization@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Sungho Bae When a port is hot-unplugged, unplug_port() nullifies port->portdev. However, concurrent TX paths (__send_to_port, put_chars) could read a stale pointer or encounter a NULL pointer dereference. Add READ_ONCE(port->portdev) and NULL checks in the TX paths. In __send_to_port(), move the out_vq assignment inside the outvq_lock and check portdev under the lock. Correspondingly, update unplug_port() to NULL out port->portdev while holding the outvq_lock to serialize with __send_to_port(). In put_chars(), return count instead of 0 on unplug to prevent the hvc layer from spinning in an infinite retry loop. Signed-off-by: Sungho Bae --- drivers/char/virtio_console.c | 37 +++++++++++++++++++++++++++++------ 1 file changed, 31 insertions(+), 6 deletions(-) diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c index bbf5b3825f12..589a12261e23 100644 --- a/drivers/char/virtio_console.c +++ b/drivers/char/virtio_console.c @@ -600,11 +600,19 @@ static ssize_t __send_to_port(struct port *port, struct scatterlist *sg, int err; unsigned long flags; unsigned int len; - - out_vq = port->out_vq; + struct ports_device *portdev; spin_lock_irqsave(&port->outvq_lock, flags); + portdev = READ_ONCE(port->portdev); + + if (!portdev) { + in_count = 0; + goto free_and_done; + } + + out_vq = port->out_vq; + reclaim_consumed_buffers(port); err = virtqueue_add_outbuf(out_vq, sg, nents, buf, GFP_ATOMIC); @@ -1110,12 +1118,24 @@ static ssize_t put_chars(u32 vtermno, const u8 *buf, size_t count) struct port *port; struct scatterlist sg[1]; struct port_buffer *pbuf; + struct ports_device *portdev; port = find_port_by_vtermno(vtermno); if (!port) return -EPIPE; - pbuf = alloc_buf(port->portdev->vdev, count, 0, GFP_ATOMIC); + /* + * Silently drop output if device hot-unplug is in progress. + * portdev was NULLed by unplug_port() after hvc_remove() was + * already called, so the hvc layer will stop invoking put_chars() + * very soon. Returning count avoids a pointless retry loop in the + * interim. + */ + portdev = READ_ONCE(port->portdev); + if (!portdev) + return count; + + pbuf = alloc_buf(portdev->vdev, count, 0, GFP_ATOMIC); if (!pbuf) return -ENOMEM; @@ -1503,11 +1523,16 @@ static void unplug_port(struct port *port) remove_port_data(port); /* - * We should just assume the device itself has gone off -- - * else a close on an open port later will try to send out a - * control message. + * Null out portdev under outvq_lock so that __send_to_port() + * cannot race: it checks port->portdev inside the same lock + * and bails out if NULL, preventing any buffer from being + * enqueued to an already torn-down virtqueue. Also prevents + * a close on an open port later from sending a stale control + * message. */ + spin_lock_irq(&port->outvq_lock); port->portdev = NULL; + spin_unlock_irq(&port->outvq_lock); sysfs_remove_group(&port->dev->kobj, &port_attribute_group); device_destroy(&port_class, port->dev->devt); -- 2.34.1