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=-5.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 E53A1C48BE5 for ; Wed, 23 Jun 2021 18:56:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D05D2611C1 for ; Wed, 23 Jun 2021 18:56:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229853AbhFWS66 (ORCPT ); Wed, 23 Jun 2021 14:58:58 -0400 Received: from m43-7.mailgun.net ([69.72.43.7]:41145 "EHLO m43-7.mailgun.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229523AbhFWS66 (ORCPT ); Wed, 23 Jun 2021 14:58:58 -0400 DKIM-Signature: a=rsa-sha256; v=1; c=relaxed/relaxed; d=mg.codeaurora.org; q=dns/txt; s=smtp; t=1624474599; h=Content-Transfer-Encoding: Content-Type: In-Reply-To: MIME-Version: Date: Message-ID: From: References: Cc: To: Subject: Sender; bh=raM5yy7Fixm9SBjgzY+GjFB9SPnrp4+WIjv/dKrKXH8=; b=GBWjoKLEgLyvYVv6zH06zlnz4iM9xsisZfTGu7XslBVa1NIHBrsK9030gFD9BmWB3LPSiJhC D9DJTQ0s6ioZS9laSg0lSXFFPE51yK4TTt/Zt2nuBlMj+gFpnLkVuElIiHFcXye6kk8ULECR bhvAocpxqXumpi8U6vjZzs3XecY= X-Mailgun-Sending-Ip: 69.72.43.7 X-Mailgun-Sid: WyI4ZWZiZiIsICJsaW51eC1yZW1vdGVwcm9jQHZnZXIua2VybmVsLm9yZyIsICJiZTllNGEiXQ== Received: from smtp.codeaurora.org (ec2-35-166-182-171.us-west-2.compute.amazonaws.com [35.166.182.171]) by smtp-out-n06.prod.us-west-2.postgun.com with SMTP id 60d383df638039e9976a6a48 (version=TLS1.2, cipher=TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256); Wed, 23 Jun 2021 18:56:31 GMT Sender: sidgup=codeaurora.org@mg.codeaurora.org Received: by smtp.codeaurora.org (Postfix, from userid 1001) id 3EC04C43217; Wed, 23 Jun 2021 18:56:31 +0000 (UTC) Received: from [192.168.1.10] (cpe-75-83-25-192.socal.res.rr.com [75.83.25.192]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) (Authenticated sender: sidgup) by smtp.codeaurora.org (Postfix) with ESMTPSA id 81904C433D3; Wed, 23 Jun 2021 18:56:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 81904C433D3 Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; dmarc=none (p=none dis=none) header.from=codeaurora.org Authentication-Results: aws-us-west-2-caf-mail-1.web.codeaurora.org; spf=fail smtp.mailfrom=sidgup@codeaurora.org Subject: Re: [PATCH v3 1/4] remoteproc: core: Move cdev add before device add To: Greg KH Cc: bjorn.andersson@linaro.org, ohad@wizery.com, linux-remoteproc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, psodagud@codeaurora.org, stable@vger.kernel.org References: <1623723671-5517-1-git-send-email-sidgup@codeaurora.org> <1623723671-5517-2-git-send-email-sidgup@codeaurora.org> <0a196786-f624-d9bb-8ef9-55c04ed57497@codeaurora.org> From: Siddharth Gupta Message-ID: <7e8ee1c3-e11e-52fc-068d-34fe036e132f@codeaurora.org> Date: Wed, 23 Jun 2021 11:56:28 -0700 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US Precedence: bulk List-ID: X-Mailing-List: linux-remoteproc@vger.kernel.org On 6/23/2021 12:27 AM, Greg KH wrote: > On Wed, Jun 16, 2021 at 11:47:01AM -0700, Siddharth Gupta wrote: >> On 6/15/2021 10:58 PM, Greg KH wrote: >>> On Tue, Jun 15, 2021 at 12:03:26PM -0700, Siddharth Gupta wrote: >>>> On 6/14/2021 9:56 PM, Greg KH wrote: >>>>> On Mon, Jun 14, 2021 at 07:21:08PM -0700, Siddharth Gupta wrote: >>>>>> When cdev_add is called after device_add has been called there is no >>>>>> way for the userspace to know about the addition of a cdev as cdev_add >>>>>> itself doesn't trigger a uevent notification, or for the kernel to >>>>>> know about the change to devt. This results in two problems: >>>>>> - mknod is never called for the cdev and hence no cdev appears on >>>>>> devtmpfs. >>>>>> - sysfs links to the new cdev are not established. >>>>>> >>>>>> The cdev needs to be added and devt assigned before device_add() is >>>>>> called in order for the relevant sysfs and devtmpfs entries to be >>>>>> created and the uevent to be properly populated. >>>>> So this means no one ever ran this code on a system that used devtmpfs? >>>>> >>>>> How was it ever tested? >>>> My testing was done with toybox + Android's ueventd ramdisk. >>>> As I mentioned in the discussion, the race became evident >>>> recently. I will make sure to test all such changes without >>>> systemd/ueventd in the future. >>> It isn't an issue of systemd/ueventd, those do not control /dev on a >>> normal system, that is what devtmpfs is for. >> I am not fully aware of when devtmpfs is enabled or not, but in >> case it is not - systemd/ueventd will create these files with >> mknod, right? > No, systemd does not create device nodes, and neither does udev. Hasn't > done so for well over 10 years now. Oh okay. I thought ueventd does it because it allows setting the node permissions through ueventd.rc: https://android.googlesource.com/platform/system/core/+/master/rootdir/ueventd.rc > >> I was even manually able to call mknod from the >> terminal when some of the remoteproc character device entries >> showed up (using major number from there, and minor number being >> the remoteproc id), and that allowed me to boot up the >> remoteprocs as well. > Yes, that is fine, but that also means that this was not working from > the very beginning :( Right. To clarify, I did this after we started seeing the problem on our devices, which led me to believe there was a race between ueventd and cdev_add(). Not sure anymore if that is not the case. > >>> And devtmpfs nodes are only created if you create a struct device >>> somewhere with a proper major/minor, which you were not doing here, so >>> you must have had a static /dev on your test systems, right? >> I am not sure of what you mean by a static /dev? Could you >> explain? In case you mean the character device would be >> non-functional, that is not the case. They have been working >> for us since the beginning. > /dev on modern systems is managed by devtmpfs, which knows to create the > device nodes when you properly register the device with the driver core. > A "static" /dev is managed by mknod from userspace, like you did "by > hand", and that is usually only done by older systems. Thanks for the explanation! As I mentioned earlier - I was under the impression that ueventd does it. I will go through our older builds where this was working (without this patch) and try to see how the dev nodes were being populated. Thanks, Sid > thanks, > > greg k-h