From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756878AbbKRUhp (ORCPT ); Wed, 18 Nov 2015 15:37:45 -0500 Received: from mx2.suse.de ([195.135.220.15]:36939 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754791AbbKRUhn (ORCPT ); Wed, 18 Nov 2015 15:37:43 -0500 Date: Wed, 18 Nov 2015 21:37:42 +0100 (CET) From: Jiri Kosina X-X-Sender: jkosina@pobox.suse.cz To: Ioan-Adrian Ratiu cc: pinglinux@gmail.com, linux-usb@vger.kernel.org, linux-input@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] hid: usbhid: hid-core: fix recursive deadlock In-Reply-To: <1447874755-8673-1-git-send-email-adi@adirat.com> Message-ID: References: <1447874755-8673-1-git-send-email-adi@adirat.com> User-Agent: Alpine 2.00 (LNX 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 18 Nov 2015, Ioan-Adrian Ratiu wrote: > The critical section protected by usbhid->lock in hid_ctrl() is too > big and in rare cases causes a recursive deadlock because of its call > to hid_input_report(). > > This deadlock reproduces on newer wacom tablets like 056a:033c because > the wacom driver in its irq handler ends up calling hid_hw_request() > from wacom_intuos_schedule_prox_event() in wacom_wac.c. What this means > is that it submits a report to reschedule a proximity read through a > sync ctrl call which grabs the lock in hid_ctrl(struct urb *urb) > before calling hid_input_report(). When the irq kicks in on the same > cpu, it also tries to grab the lock resulting in a recursive deadlock. > > The proper fix is to shrink the critical section in hid_ctrl() to > protect only the instructions which modify usbhid, thus move the lock > after the hid_input_report() call and the deadlock dissapears. I think the proper fix actually is to spin_lock_irqsave() in hid_ctrl(), isn't it? -- Jiri Kosina SUSE Labs