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[209.132.180.67]) by mx.google.com with ESMTP id 26si1214464oiz.107.2020.03.26.09.32.54; Thu, 26 Mar 2020 09:33:10 -0700 (PDT) Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67; Authentication-Results: mx.google.com; spf=pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=fail (p=NONE sp=NONE dis=NONE) header.from=intel.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727846AbgCZQbN (ORCPT + 99 others); Thu, 26 Mar 2020 12:31:13 -0400 Received: from mga07.intel.com ([134.134.136.100]:50938 "EHLO mga07.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726163AbgCZQbM (ORCPT ); Thu, 26 Mar 2020 12:31:12 -0400 IronPort-SDR: vubi7NXeJQLO0L/z4x6Xhe9jprk9bqrdP1U/anrnhFcqqkg9oVif09ip68zatzG0Zxgy7GJEK2 6eSzugGUPomg== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga003.fm.intel.com ([10.253.24.29]) by orsmga105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 26 Mar 2020 09:31:12 -0700 IronPort-SDR: gqjvMPmgw1AKUgRs3sQHKGYc7rsAGXh8sjXEHJi8RSvnm6nXpLH27WprIdC+RxBuJiJ0tg630O 5hZon0IiRinw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,309,1580803200"; d="scan'208";a="293681073" Received: from smile.fi.intel.com (HELO smile) ([10.237.68.40]) by FMSMGA003.fm.intel.com with ESMTP; 26 Mar 2020 09:31:08 -0700 Received: from andy by smile with local (Exim 4.93) (envelope-from ) id 1jHVPS-00DBWz-Uu; Thu, 26 Mar 2020 18:31:10 +0200 Date: Thu, 26 Mar 2020 18:31:10 +0200 From: Andy Shevchenko To: Grant Likely Cc: Saravana Kannan , a.hajda@samsung.com, artem.bityutskiy@linux.intel.com, balbi@kernel.org, broonie@kernel.org, fntoth@gmail.com, gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, peter.ujfalusi@ti.com, rafael@kernel.org, kernel-team@android.com, nd Subject: Re: [PATCH v3] driver core: Break infinite loop when deferred probe can't be satisfied Message-ID: <20200326163110.GD1922688@smile.fi.intel.com> References: <20200324175719.62496-1-andriy.shevchenko@linux.intel.com> <20200325032901.29551-1-saravanak@google.com> <20200325125120.GX1922688@smile.fi.intel.com> <295d25de-f01e-26de-02d6-1ac0c149d828@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <295d25de-f01e-26de-02d6-1ac0c149d828@arm.com> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 26, 2020 at 03:01:22PM +0000, Grant Likely wrote: > On 25/03/2020 12:51, Andy Shevchenko wrote: > > On Tue, Mar 24, 2020 at 08:29:01PM -0700, Saravana Kannan wrote: > > > On Tue, Mar 24, 2020 at 5:38 AM Andy Shevchenko wrote: > > > > 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. > > > > > > Hi Andy, > > > > > > I'm trying to understand this sequence of steps. Sorry if the questions > > > are stupid -- I'm not very familiar with USB/PCI stuff. > > > > Thank you for looking into this. My answer below. > > > > As a first thing I would like to tell that there is another example of bad > > behaviour of deferred probe with no relation to USB. The proposed change also > > fixes that one (however, less possible to find in real life). > > > > > > ---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... > > > > > > Ok, dwc3.0.auto is the only unprobed device at this point? > > > > Correct. > > > > > > [ 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 > > > > > > So where did this dwc3.0.auto.ulpi come from? > > > > > Looks like the device is created by dwc3_probe() through this call flow: > > > dwc3_probe() -> dwc3_core_init() -> dwc3_core_ulpi_init() -> > > > dwc3_ulpi_init() -> ulpi_register_interface() -> ulpi_register() > > > > Correct. > > > > > > [ 22.276697] platform dwc3.0.auto: Driver dwc3 requests probe deferral > > > > > > Can you please point me to which code patch actually caused the probe > > > deferral? > > > > Sure, it's in drd.c. > > > > if (device_property_read_string(dev, "linux,extcon-name", &name) == 0) { > > edev = extcon_get_extcon_dev(name); > > if (!edev) > > return ERR_PTR(-EPROBE_DEFER); > > return edev; > > } > > > > > > ...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 > > > > > > I'm not fully aware of all the USB implications, but if extcon is > > > needed, why can't that check be done before we add and probe the ulpi > > > device? That'll avoid this whole "fake" probing and avoid the counter > > > increase. And avoid the need for this patch that's touching the code > > > code that's already a bit delicate. > > > > > Also, with my limited experience with all the possible drivers in the > > > kernel, it's weird that the ulpi device is added and probed before we > > > make sure the parent device (dwc3.0.auto) can actually probe > > > successfully. > > > > As I said above the deferred probe trigger has flaw on its own. > > Even if we fix for USB case, there is (and probably will be) others. > > Right here is the driver design bug. A driver's probe() hook should *not* > return -EPROBE_DEFER after already creating child devices which may have > already been probed. Any documentation statement for this requirement? By the way, I may imagine other mechanisms that probe the driver on other CPU at the same time (let's consider parallel modprobes). The current code has a flaw with that. > It can be solved by refactoring the driver probe routine. If a resource is > required to be present, then check that it is available early; before > registering child devices. We fix one and leave others. > The proposed solution to modify driver core is fragile and susceptible to > side effects from other probe paths. I don't think it is the right approach. Have you tested it on your case? Does it fix the issue? -- With Best Regards, Andy Shevchenko