Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932268AbbLBAAe (ORCPT ); Tue, 1 Dec 2015 19:00:34 -0500 Received: from mail-ob0-f177.google.com ([209.85.214.177]:33071 "EHLO mail-ob0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932128AbbLBAAc (ORCPT ); Tue, 1 Dec 2015 19:00:32 -0500 MIME-Version: 1.0 In-Reply-To: References: <1447874755-8673-1-git-send-email-adi@adirat.com> <1448050742-10777-1-git-send-email-adi@adirat.com> From: Ping Cheng Date: Tue, 1 Dec 2015 16:00:12 -0800 Message-ID: Subject: Re: [PATCH v2] hid: usbhid: hid-core: fix recursive deadlock To: Jiri Kosina Cc: Ioan-Adrian Ratiu , "linux-usb@vger.kernel.org" , linux-input , "linux-kernel@vger.kernel.org" , joshc@ni.com, Benjamin Tissoires Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1982 Lines: 44 Hi Jiri, On Tue, Dec 1, 2015 at 8:36 AM, Jiri Kosina wrote: > On Fri, 20 Nov 2015, Ioan-Adrian Ratiu wrote: > >> The critical section protected by usbhid->lock in hid_ctrl() is too >> big and because of this it causes a recursive deadlock. "Too big" means >> the case statement and the call to hid_input_report() do not need to be >> protected by the spinlock (no URB operations are done inside them). >> >> The deadlock happens because in certain rare cases drivers try to grab >> the lock while handling the ctrl irq which grabs the lock before them >> as described above. For example newer wacom tablets like 056a:033c try >> to reschedule proximity reads from wacom_intuos_schedule_prox_event() >> calling hid_hw_request() -> usbhid_request() -> usbhid_submit_report() >> which tries to grab the usbhid lock already held by hid_ctrl(). >> >> There are two ways to get out of this deadlock: >> 1. Make the drivers work "around" the ctrl critical region, in the >> wacom case for ex. by delaying the scheduling of the proximity read >> request itself to a workqueue. >> 2. Shrink the critical region so the usbhid lock protects only the >> instructions which modify usbhid state, calling hid_input_report() >> with the spinlock unlocked, allowing the device driver to grab the >> lock first, finish and then grab the lock afterwards in hid_ctrl(). >> >> This patch implements the 2nd solution. >> >> Signed-off-by: Ioan-Adrian Ratiu > > Applied to for-4.5/core branch. Thanks, Since wacom_intuos_schedule_prox_event() was introduced on March 5, 2015, the call was first used in kernel 3.19. Shouldn't we back-port this patch to other stable versions? Thank you. Ping -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/