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=-8.2 required=3.0 tests=DKIM_ADSP_CUSTOM_MED, FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 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 225BAC4332B for ; Thu, 19 Mar 2020 00:03:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D86AB20754 for ; Thu, 19 Mar 2020 00:03:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727112AbgCSAD0 (ORCPT ); Wed, 18 Mar 2020 20:03:26 -0400 Received: from mailfilter02-out31.webhostingserver.nl ([141.138.168.75]:58827 "EHLO mailfilter02-out31.webhostingserver.nl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726776AbgCSAD0 (ORCPT ); Wed, 18 Mar 2020 20:03:26 -0400 X-Greylist: delayed 964 seconds by postgrey-1.27 at vger.kernel.org; Wed, 18 Mar 2020 20:03:24 EDT X-Halon-ID: ce0cb097-6972-11ea-a736-001a4a4cb922 Received: from s198.webhostingserver.nl (unknown [195.211.72.171]) by mailfilter02.webhostingserver.nl (Halon) with ESMTPSA id ce0cb097-6972-11ea-a736-001a4a4cb922; Thu, 19 Mar 2020 00:47:19 +0100 (CET) Received: from cust-178-250-146-69.breedbanddelft.nl ([178.250.146.69] helo=[10.8.0.6]) by s198.webhostingserver.nl with esmtpa (Exim 4.92.3) (envelope-from ) id 1jEiP9-003Hky-2e; Thu, 19 Mar 2020 00:47:19 +0100 Subject: Re: [PATCH v1 1/3] driver core: Break infinite loop when deferred probe can't be satisfied To: Andy Shevchenko , Greg Kroah-Hartman , "Rafael J. Wysocki" , linux-kernel@vger.kernel.org Cc: Artem Bityutskiy , Grant Likely , Peter Ujfalusi , Mark Brown , Felipe Balbi , Andrzej Hajda References: <20200309141111.40576-1-andriy.shevchenko@linux.intel.com> From: Ferry Toth Message-ID: <5b751d5b-53ec-9c99-d977-68b71dd303f8@gmail.com> Date: Thu, 19 Mar 2020 00:47:18 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200309141111.40576-1-andriy.shevchenko@linux.intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-SendingUser: hidden X-SendingServer: hidden X-Antivirus-Scanner: Clean mail though you should still use an Antivirus X-Authenticated-Id: hidden X-SendingUser: hidden X-SendingServer: hidden Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Op 09-03-2020 om 15:11 schreef Andy Shevchenko: > Consider the following scenario. > > The main driver of USB OTG controller (dwc3-pci), which has the following > functional dependencies on certain platform: > - ULPI (tusb1210) > - extcon (tested with extcon-intel-mrfld) > > Note, that first driver, tusb1210, is available at the moment of > dwc3-pci probing, while extcon-intel-mrfld is built as a module and > won't appear till user space does something about it. > > This is depicted by kernel configuration excerpt: > > CONFIG_PHY_TUSB1210=y > CONFIG_USB_DWC3=y > CONFIG_USB_DWC3_ULPI=y > CONFIG_USB_DWC3_DUAL_ROLE=y > CONFIG_USB_DWC3_PCI=y > CONFIG_EXTCON_INTEL_MRFLD=m > > In the Buildroot environment the modules are probed by alphabetical ordering > of their modaliases. The latter comes to the case when USB OTG driver will be > probed first followed by extcon one. > > So, if the platform anticipates extcon device to be appeared, in the above case > we will get deferred probe of USB OTG, because of ordering. > > Since current implementation, done by the commit 58b116bce136 ("drivercore: > deferral race condition fix") counts the amount of triggered deferred probe, > we never advance the situation -- the change makes it to be an infinite loop. > > ---8<---8<--- > > [ 22.187127] driver_deferred_probe_trigger <<< 1 > > ...here is the late initcall triggers deferred probe... > > [ 22.191725] platform dwc3.0.auto: deferred_probe_work_func in deferred list > > ...dwc3.0.auto is the only device in the deferred list... > > [ 22.198727] platform dwc3.0.auto: deferred_probe_work_func 1 <<< counter 1 > > ...the counter before mutex is unlocked is kept the same... > > [ 22.205663] platform dwc3.0.auto: Retrying from deferred list > > ...mutes has been unlocked, we try to re-probe the driver... > > [ 22.211487] bus: 'platform': driver_probe_device: matched device dwc3.0.auto with driver dwc3 > [ 22.220060] bus: 'platform': really_probe: probing driver dwc3 with device dwc3.0.auto > [ 22.238735] bus: 'ulpi': driver_probe_device: matched device dwc3.0.auto.ulpi with driver tusb1210 > [ 22.247743] bus: 'ulpi': really_probe: probing driver tusb1210 with device dwc3.0.auto.ulpi > [ 22.256292] driver: 'tusb1210': driver_bound: bound to device 'dwc3.0.auto.ulpi' > [ 22.263723] driver_deferred_probe_trigger <<< 2 > > ...the dwc3.0.auto probes ULPI, we got successful bound and bumped counter... > > [ 22.268304] bus: 'ulpi': really_probe: bound device dwc3.0.auto.ulpi to driver tusb1210 > [ 22.276697] platform dwc3.0.auto: Driver dwc3 requests probe deferral > > ...but extcon driver is still missing... > > [ 22.283174] platform dwc3.0.auto: Added to deferred list > [ 22.288513] platform dwc3.0.auto: driver_deferred_probe_add_trigger local counter: 1 new counter 2 > > ...and since we had a successful probe, we got counter mismatch... > > [ 22.297490] driver_deferred_probe_trigger <<< 3 > [ 22.302074] platform dwc3.0.auto: deferred_probe_work_func 2 <<< counter 3 > > ...at the end we have a new counter and loop repeats again, see 22.198727... > > ---8<---8<--- > > Revert of the commit helps, but it is probably not helpful for the initially > found regression. Artem Bityutskiy suggested to use counter of the successful > probes instead. This fixes above mentioned case and shouldn't prevent driver > to reprobe deferred ones. > > Fixes: 58b116bce136 ("drivercore: deferral race condition fix") > Suggested-by: Artem Bityutskiy > Cc: Grant Likely > Cc: Peter Ujfalusi > Cc: Greg Kroah-Hartman > Cc: Mark Brown > Cc: Felipe Balbi > Cc: Andrzej Hajda > Signed-off-by: Andy Shevchenko Tested-by: Ferry Toth > --- > drivers/base/dd.c | 39 +++++++++++++++++++++------------------ > 1 file changed, 21 insertions(+), 18 deletions(-) > > diff --git a/drivers/base/dd.c b/drivers/base/dd.c > index b25bcab2a26b..43720beb5300 100644 > --- a/drivers/base/dd.c > +++ b/drivers/base/dd.c > @@ -53,7 +53,6 @@ > static DEFINE_MUTEX(deferred_probe_mutex); > static LIST_HEAD(deferred_probe_pending_list); > static LIST_HEAD(deferred_probe_active_list); > -static atomic_t deferred_trigger_count = ATOMIC_INIT(0); > static struct dentry *deferred_devices; > static bool initcalls_done; > > @@ -147,17 +146,6 @@ static bool driver_deferred_probe_enable = false; > * This functions moves all devices from the pending list to the active > * list and schedules the deferred probe workqueue to process them. It > * should be called anytime a driver is successfully bound to a device. > - * > - * Note, there is a race condition in multi-threaded probe. In the case where > - * more than one device is probing at the same time, it is possible for one > - * probe to complete successfully while another is about to defer. If the second > - * depends on the first, then it will get put on the pending list after the > - * trigger event has already occurred and will be stuck there. > - * > - * The atomic 'deferred_trigger_count' is used to determine if a successful > - * trigger has occurred in the midst of probing a driver. If the trigger count > - * changes in the midst of a probe, then deferred processing should be triggered > - * again. > */ > static void driver_deferred_probe_trigger(void) > { > @@ -170,7 +158,6 @@ static void driver_deferred_probe_trigger(void) > * into the active list so they can be retried by the workqueue > */ > mutex_lock(&deferred_probe_mutex); > - atomic_inc(&deferred_trigger_count); > list_splice_tail_init(&deferred_probe_pending_list, > &deferred_probe_active_list); > mutex_unlock(&deferred_probe_mutex); > @@ -350,6 +337,19 @@ static void __exit deferred_probe_exit(void) > } > __exitcall(deferred_probe_exit); > > +/* > + * Note, there is a race condition in multi-threaded probe. In the case where > + * more than one device is probing at the same time, it is possible for one > + * probe to complete successfully while another is about to defer. If the second > + * depends on the first, then it will get put on the pending list after the > + * trigger event has already occurred and will be stuck there. > + * > + * The atomic 'probe_okay' is used to determine if a successful probe has > + * occurred in the midst of probing another driver. If the count changes in > + * the midst of a probe, then deferred processing should be triggered again. > + */ > +static atomic_t probe_okay = ATOMIC_INIT(0); > + > /** > * device_is_bound() - Check if device is bound to a driver > * @dev: device to check > @@ -375,6 +375,7 @@ static void driver_bound(struct device *dev) > pr_debug("driver: '%s': %s: bound to device '%s'\n", dev->driver->name, > __func__, dev_name(dev)); > > + atomic_inc(&probe_okay); > klist_add_tail(&dev->p->knode_driver, &dev->driver->p->klist_devices); > device_links_driver_bound(dev); > > @@ -481,18 +482,18 @@ static atomic_t probe_count = ATOMIC_INIT(0); > static DECLARE_WAIT_QUEUE_HEAD(probe_waitqueue); > > static void driver_deferred_probe_add_trigger(struct device *dev, > - int local_trigger_count) > + int local_probe_okay_count) > { > driver_deferred_probe_add(dev); > /* Did a trigger occur while probing? Need to re-trigger if yes */ > - if (local_trigger_count != atomic_read(&deferred_trigger_count)) > + if (local_probe_okay_count != atomic_read(&probe_okay)) > driver_deferred_probe_trigger(); > } > > static int really_probe(struct device *dev, struct device_driver *drv) > { > int ret = -EPROBE_DEFER; > - int local_trigger_count = atomic_read(&deferred_trigger_count); > + int local_probe_okay_count = atomic_read(&probe_okay); > bool test_remove = IS_ENABLED(CONFIG_DEBUG_TEST_DRIVER_REMOVE) && > !drv->suppress_bind_attrs; > > @@ -509,7 +510,7 @@ static int really_probe(struct device *dev, struct device_driver *drv) > > ret = device_links_check_suppliers(dev); > if (ret == -EPROBE_DEFER) > - driver_deferred_probe_add_trigger(dev, local_trigger_count); > + driver_deferred_probe_add_trigger(dev, local_probe_okay_count); > if (ret) > return ret; > > @@ -619,7 +620,7 @@ static int really_probe(struct device *dev, struct device_driver *drv) > case -EPROBE_DEFER: > /* Driver requested deferred probing */ > dev_dbg(dev, "Driver %s requests probe deferral\n", drv->name); > - driver_deferred_probe_add_trigger(dev, local_trigger_count); > + driver_deferred_probe_add_trigger(dev, local_probe_okay_count); > break; > case -ENODEV: > case -ENXIO: > @@ -1148,6 +1149,8 @@ static void __device_release_driver(struct device *dev, struct device *parent) > dev_pm_set_driver_flags(dev, 0); > > klist_remove(&dev->p->knode_driver); > + atomic_dec(&probe_okay); > + > device_pm_check_callbacks(dev); > if (dev->bus) > blocking_notifier_call_chain(&dev->bus->p->bus_notifier, >