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=-6.0 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 9A20AC48BE6 for ; Wed, 16 Jun 2021 05:58:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7DA286109D for ; Wed, 16 Jun 2021 05:58:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231252AbhFPGA6 (ORCPT ); Wed, 16 Jun 2021 02:00:58 -0400 Received: from mail.kernel.org ([198.145.29.99]:57486 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231200AbhFPGA5 (ORCPT ); Wed, 16 Jun 2021 02:00:57 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 750176128C; Wed, 16 Jun 2021 05:58:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1623823132; bh=mbCodwMIm1uO6V8GxochPay+jWIcegWFL544VUVwHXg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=M5vdOsIe2Zer92PkoDT5IunwubV5UQ1Vs7rNcq2Ea3wSGn7LJIEZLsHqaSeh7Q2wh UYg+Pvtp6gWzOE79brNsTv5CW5vKJV7rMKwVIl6VoHMMs12qrEdR6Sr0L172tju/Fd pPcZ2MXA+slC0xJ12ww6k0enzlONfls4e+4MJJWY= Date: Wed, 16 Jun 2021 07:58:48 +0200 From: Greg KH To: Siddharth Gupta 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 Subject: Re: [PATCH v3 1/4] remoteproc: core: Move cdev add before device add Message-ID: 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <0a196786-f624-d9bb-8ef9-55c04ed57497@codeaurora.org> Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org 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. 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? thanks, greg k-h