From patchwork Thu Mar 4 04:10:53 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Pete Zaitcev X-Patchwork-Id: 12115427 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 922BEC433DB for ; Thu, 4 Mar 2021 04:14:05 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 591DA601FF for ; Thu, 4 Mar 2021 04:14:05 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233192AbhCDEM4 (ORCPT ); Wed, 3 Mar 2021 23:12:56 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:42156 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232952AbhCDEMX (ORCPT ); Wed, 3 Mar 2021 23:12:23 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1614831057; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding; bh=IXs3zF75SzOR3sX6dltuZ3LkzNt/Igst3EtKMWfws+M=; b=a0+SGkM7PGR4cG7SSg/hprFe0aM7/maS5dj6kEsbKsCRq1wK2+VuZRWnizHehXqkQuVcTp yat7yWhsu3t11rPiFxzIH/6BMs+KXtGk4lPkBSsP3YVgjCf/SdZ10N0g4T1kEi/wYtZpRM 5cnfBiwmEhXzmOwyHy3Sy7qzEy3Pjwc= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-112-C_sMAQWXPqqKw81VtdMo7A-1; Wed, 03 Mar 2021 23:10:55 -0500 X-MC-Unique: C_sMAQWXPqqKw81VtdMo7A-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 1DE57801980; Thu, 4 Mar 2021 04:10:54 +0000 (UTC) Received: from suzdal.zaitcev.lan (ovpn-114-139.phx2.redhat.com [10.3.114.139]) by smtp.corp.redhat.com (Postfix) with ESMTP id B4B526A8E4; Thu, 4 Mar 2021 04:10:53 +0000 (UTC) Date: Wed, 3 Mar 2021 22:10:53 -0600 From: Pete Zaitcev To: gregkh@linuxfoundation.org, linux-usb@vger.kernel.org Cc: Pete Zaitcev , qiang.zhang@windriver.com Subject: [PATCH] USB: usblp: fix a hang in poll() if disconnected Message-ID: <20210303221053.1cf3313e@suzdal.zaitcev.lan> Organization: Red Hat, Inc. MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org Apparently an application that opens a device and calls select() on it, will hang if the decice is disconnected. It's a little surprising that we had this bug for 15 years, but apparently nobody ever uses select() with a printer: only write() and read(), and those work fine. Well, you can also select() with a timeout. The fix is modeled after devio.c. A few other drivers check the condition first, then do not add the wait queue in case the device is disconnected. We doubt that's completely race-free. So, this patch adds the process first, then locks properly and checks for the disconnect. Reviewed-by: Zqiang Signed-off-by: Pete Zaitcev --- drivers/usb/class/usblp.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-) diff --git a/drivers/usb/class/usblp.c b/drivers/usb/class/usblp.c index fd87405adbed..9596e4279294 100644 --- a/drivers/usb/class/usblp.c +++ b/drivers/usb/class/usblp.c @@ -494,16 +494,24 @@ static int usblp_release(struct inode *inode, struct file *file) /* No kernel lock - fine */ static __poll_t usblp_poll(struct file *file, struct poll_table_struct *wait) { - __poll_t ret; + struct usblp *usblp = file->private_data; + __poll_t ret = 0; unsigned long flags; - struct usblp *usblp = file->private_data; /* Should we check file->f_mode & FMODE_WRITE before poll_wait()? */ poll_wait(file, &usblp->rwait, wait); poll_wait(file, &usblp->wwait, wait); + + mutex_lock(&usblp->mut); + if (!usblp->present) + ret |= EPOLLHUP; + mutex_unlock(&usblp->mut); + spin_lock_irqsave(&usblp->lock, flags); - ret = ((usblp->bidir && usblp->rcomplete) ? EPOLLIN | EPOLLRDNORM : 0) | - ((usblp->no_paper || usblp->wcomplete) ? EPOLLOUT | EPOLLWRNORM : 0); + if (usblp->bidir && usblp->rcomplete) + ret |= EPOLLIN | EPOLLRDNORM; + if (usblp->no_paper || usblp->wcomplete) + ret |= EPOLLOUT | EPOLLWRNORM; spin_unlock_irqrestore(&usblp->lock, flags); return ret; }