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[23.128.96.18]) by mx.google.com with ESMTP id k16si10110473eja.149.2020.06.09.00.33.22; Tue, 09 Jun 2020 00:33:45 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.s=20161025 header.b=G9DZqTNs; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726965AbgFIHan (ORCPT + 99 others); Tue, 9 Jun 2020 03:30:43 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:58594 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726099AbgFIHal (ORCPT ); Tue, 9 Jun 2020 03:30:41 -0400 Received: from mail-ot1-x343.google.com (mail-ot1-x343.google.com [IPv6:2607:f8b0:4864:20::343]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6F1ECC03E97C for ; Tue, 9 Jun 2020 00:30:41 -0700 (PDT) Received: by mail-ot1-x343.google.com with SMTP id 97so4473614otg.3 for ; Tue, 09 Jun 2020 00:30:41 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=gLy6eUAtGnvNRuBVPLvPPB4x/ePRcKM+zvqM1T2LZ1g=; b=G9DZqTNsJ9rRPo1qFjn0ejXsJ/PEaeRaEI3op7x6r3leM1lkET9P1YKIouZkm78mNU IF4AfftHN6zFAGasCVGrKTwwFFlMHYabdg01TMhJKsONUZPZSOZuAu2vuLAcsBzJg65Q SW0nqO3ImY/DSaRUDo7g+Et3OjamaO6pPleDy/2S/+nde/jU327BhOTor2wa7nJ71D/N 1HKpLYOzQLE5/4rtINe2uez0Hw3hMBetrNlqX/wcJLLLzHVD+3DN3KoKTgAHImXaVZ88 FN+A/8Jn20aTRw0gFqIPuOO5DT1pvAFe5xQJSqcEXYGrf0vMCZ3Fh+mHF1t/WXN9HcEN kM6g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=gLy6eUAtGnvNRuBVPLvPPB4x/ePRcKM+zvqM1T2LZ1g=; b=FQcepRFQoxaTpBFwO4zdqfukkZ/XfjYF6TPdLpCrO/Lo0QX7jgJYR9de3khlYx4HnK uln3pB8wVjpcrlCNPLyVPK+4ybQoa9SP+MDYXM23YqWMH3cj7FcAejNasNCp+osZQigS PGraYwRJ2neXrUSoeuGtmwOFGv5yXChenkkGS+4dzMeD9pgbZTcoOF6bywcjrBzM8J1q 2Fn+I+Jb9+xgWRSBkeG1tsIR02udKB5ypqOGU82O2QfZe8Zpnwe2CYgrlSkx3uOOdw1A 59DKEX8TSbwq3E2QL+gZjM4ny6yfDQgVJ/actWNaOSV9Mwgto32c32lEvf0UnxNlUBe2 +gVw== X-Gm-Message-State: AOAM53305aTfk+GHIJVB6qqNiKcaqYqXbXHDECK4gEbAs4LFkscP61Ro 19Ie6wboC3qXPX9vlm/KO3pyj8LO7UHpe7OYt7yqgg== X-Received: by 2002:a9d:6048:: with SMTP id v8mr15461661otj.231.1591687840358; Tue, 09 Jun 2020 00:30:40 -0700 (PDT) MIME-Version: 1.0 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> <20200326163110.GD1922688@smile.fi.intel.com> <20200608091712.GA28093@pengutronix.de> <437de51b-37e9-d8d1-19c7-137a9265bf45@samsung.com> <20200609064511.7nek2rhk6ebfjaia@pengutronix.de> In-Reply-To: <20200609064511.7nek2rhk6ebfjaia@pengutronix.de> From: Saravana Kannan Date: Tue, 9 Jun 2020 00:30:04 -0700 Message-ID: Subject: Re: [PATCH v3] driver core: Break infinite loop when deferred probe can't be satisfied To: Marco Felsch Cc: Andrzej Hajda , Andy Shevchenko , Grant Likely , Artem Bityutskiy , Felipe Balbi , Mark Brown , Ferry Toth , Greg Kroah-Hartman , LKML , Linux PM , Peter Ujfalusi , "Rafael J. Wysocki" , Android Kernel Team , nd , kernel@pengutronix.de Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jun 8, 2020 at 11:45 PM Marco Felsch wrote: > > On 20-06-08 13:11, Andrzej Hajda wrote: > > > > On 08.06.2020 11:17, Marco Felsch wrote: > > > On 20-03-26 18:31, Andy Shevchenko wrote: > > >> 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. > > > Hi, > > > > > > sorry for picking this up again but I stumbled above the same issue > > > within the driver imx/drm driver which is using the component framework. > > > I end up in a infinity boot loop if I enabled the HDMI (which is the > > > DesignWare bridge device) and the LVDS support and the LVDS bind return > > > with EPROBE_DEFER. There are no words within the component framework docs > > > which says that this is forbidden. Of course we can work-around the > > > driver-core framework but IMHO this shouldn't be the way to go. I do not > > > say that we should revert the commit introducing the regression but we > > > should address this not only by extending the docs since the most > > > drm-drivers are using the component framework and can end up in the same > > > situation. > > > > I am not sure why do you think this is similar issue. > > Because I see trying to bind the device over and over.. > > > Please describe the issue in more detail. Which drivers defers probe and > > why, and why do you have infinite loop. > > As said I'm currently on the imx-drm driver. The iMX6 devices are > using the synopsis HDMI IP core and so they are using this bridge device > driver (drivers/gpu/drm/bridge/synopsys/). The imx-drm driver can be > build module wise. As example I enabled the LDB and the HDMI support. > The HDMI driver is composed as platform driver with different > (sub-)drivers and devices. Those devices are populated by the HDMI core > driver _probe() function and triggers a driver_deferred_probe_trigger() > after the driver successfully probed. The LDB driver bind() returns > -EPROBE_DEFER because the panel we are looking for depends on a defered > regulator device. Now the defered probe code tries to probe the defered > devices again because the local-trigger count was changed by the HDMI > driver and we are in the never ending loop. > > > In general deferring probe from bind is not forbidden, but it should be > > used carefully (as everything in kernel :) ). Fixing deferring probe > > issues in many cases it is a matter of figuring out 'dependency loops' > > and breaking them by splitting device initialization into more than one > > phase. > > We are on the way of splitting the imx-drm driver but there are many > other DRM drivers using the component framework. As far as I can see the > sunxi8 driver is component based and uses the same HDMI driver. I'm with > Andy that we should fix that on the common/core place. I'm not opposed to fixing this at the common/core level if that's possible, but Andy's patch still has a bug where it might never probe a device. I still haven't seen an answer to this. https://lore.kernel.org/lkml/CAGETcx_3+YH_LmNUCAAk1OaXk6noHEXxcE+ckkoBqKJJhtpDjQ@mail.gmail.com/ -Saravana