From mboxrd@z Thu Jan 1 00:00:00 1970 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=-3.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no 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 E7B8FC3A589 for ; Thu, 15 Aug 2019 14:47:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C42C020656 for ; Thu, 15 Aug 2019 14:47:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730645AbfHOOrq (ORCPT ); Thu, 15 Aug 2019 10:47:46 -0400 Received: from iolanthe.rowland.org ([192.131.102.54]:58254 "HELO iolanthe.rowland.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1729924AbfHOOrq (ORCPT ); Thu, 15 Aug 2019 10:47:46 -0400 Received: (qmail 2558 invoked by uid 2102); 15 Aug 2019 10:47:45 -0400 Received: from localhost (sendmail-bs@127.0.0.1) by localhost with SMTP; 15 Aug 2019 10:47:45 -0400 Date: Thu, 15 Aug 2019 10:47:45 -0400 (EDT) From: Alan Stern X-X-Sender: stern@iolanthe.rowland.org To: Greg KH cc: Andrey Konovalov , Oliver Neukum , syzkaller-bugs , USB list Subject: Re: [PATCH] USB: rio500: Fix lockdep violation In-Reply-To: <20190815124821.GA25619@kroah.com> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-usb-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-usb@vger.kernel.org On Thu, 15 Aug 2019, Greg KH wrote: > On Thu, Aug 08, 2019 at 02:23:00PM -0400, Alan Stern wrote: > > On Thu, 8 Aug 2019, Greg KH wrote: > > > > > On Thu, Aug 08, 2019 at 01:34:08PM -0400, Alan Stern wrote: > > > > The syzbot fuzzer found a lockdep violation in the rio500 driver: > > > > > > > > ====================================================== > > > > WARNING: possible circular locking dependency detected > > > > 5.3.0-rc2+ #23 Not tainted > > > > ------------------------------------------------------ > > > > syz-executor.2/20386 is trying to acquire lock: > > > > 00000000772249c6 (rio500_mutex){+.+.}, at: open_rio+0x16/0xc0 > > > > drivers/usb/misc/rio500.c:64 > > > > > > > > but task is already holding lock: > > > > 00000000d3e8f4b9 (minor_rwsem){++++}, at: usb_open+0x23/0x270 > > > > drivers/usb/core/file.c:39 > > > > > > > > which lock already depends on the new lock. > > > > > > > > The problem is that the driver's open_rio() routine is called while > > > > the usbcore's minor_rwsem is locked for reading, and it acquires the > > > > rio500_mutex; whereas conversely, probe_rio() and disconnect_rio() > > > > first acquire the rio500_mutex and then call usb_register_dev() or > > > > usb_deregister_dev(), which lock minor_rwsem for writing. > > > > > > > > The correct ordering of acquisition should be: minor_rwsem first, then > > > > rio500_mutex (since the locking in open_rio() cannot be changed). > > > > Thus, the probe and disconnect routines should avoid holding > > > > rio500_mutex while doing their registration and deregistration. > > > > > > > > This patch adjusts the code in those two routines to do just that. It > > > > also relies on the fact that the probe and disconnect routines are > > > > protected by the device mutex, so the initial test of rio->present > > > > needs no extra locking. > > > > > > > > Reported-by: syzbot+7bbcbe9c9ff0cd49592a@syzkaller.appspotmail.com > > > > Signed-off-by: Alan Stern > > > > Fixes: d710734b0677 ("USB: rio500: simplify locking") > > > > CC: Oliver Neukum > > > > CC: > > > > > > > > --- > > > > > > > > This patch is different from the one I posted earlier. I realized that > > > > we don't want to register the device's char file until after the > > > > buffers have been allocated. > > > > > > Should I revert Oliver's patch? > > > > Sorry, I should have explained more clearly: This goes on top of > > Oliver's patch. In fact, Oliver's patch is the one listed in the > > Fixes: tag. > > > > You do not need to apply Oliver's reversion. Assuming he agrees that > > this patch is correct, of course. > > Ok, I applied the revert, and that's in 5.3-rc4. So of course this does > not apply :) > > Shoudl I revert the revert and then apply this? I will if I can get an > ack from Oliver... Either that or else Oliver and I can squash the two patches into one. Alan Stern