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=-6.1 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 92A31C48BC2 for ; Wed, 23 Jun 2021 07:27:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7B58F6128A for ; Wed, 23 Jun 2021 07:27:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229928AbhFWHaC (ORCPT ); Wed, 23 Jun 2021 03:30:02 -0400 Received: from mail.kernel.org ([198.145.29.99]:59654 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229660AbhFWHaC (ORCPT ); Wed, 23 Jun 2021 03:30:02 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 7FC0D61076; Wed, 23 Jun 2021 07:27:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1624433264; bh=MfGpAhkgNAsV4Gs6J3HXShXQ6oCjPOD50RyhMvI5TIg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=VL3P8zhD1J20JIY2+okRVn52pWiyX0awT2ZEVB1iqKyPEBYhY9PaQjYqUQzPkriup d9d1+2/QNqASXUYg+5eheF++kEPxPVMbHSwrOsoBQbv/e3FSK+pudi4Plpyu9fxbpe GV+0b11T757IsJ8cMWyS/7IkjBHHTatjN+TCeVsw= Date: Wed, 23 Jun 2021 09:27:41 +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: Precedence: bulk List-ID: X-Mailing-List: linux-remoteproc@vger.kernel.org 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. > 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 :( > > 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, greg k-h 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=-4.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,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 E20F8C4743C for ; Wed, 23 Jun 2021 07:29:35 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id B25686101D for ; Wed, 23 Jun 2021 07:29:35 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B25686101D Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=Tng5fcbGbFjrAU8HcwSKT1lC3YmkAOmamVRH5ARkn7I=; b=EjeUI5cNE+98KF 6xKicGEcl6LpNM/gsLrFnV3cpTksI7YMaM8cD/ur4HrasqUuaeZuxw5dJ1o4ntJwPR+9f1H7xajt2 AuHY4dCJaxr36/Of4Td8iCCZqV/Q2GA6cm22Znv2IHztRNwgJuN8WPuaGtoCZXVOiwwZjwtvaOvOi j3noC4zkoW5k5wfT9Cw1qHZO1qYLz/KBzUaf6htHhGew7FzCT8MkViZ2/lxb/+FwshGsY8EAccMB4 Pu5T/DWJN5ViU2JRKXm9RV+L8l7HdNvuDAZ8AI8NTCMjKkAez/o20PkLn9HfLL6zGgzv+cfN5HkHi y0q656joWF8xGXbLmr/g==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1lvxIa-009jOX-KO; Wed, 23 Jun 2021 07:27:48 +0000 Received: from mail.kernel.org ([198.145.29.99]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1lvxIW-009jNp-J5 for linux-arm-kernel@lists.infradead.org; Wed, 23 Jun 2021 07:27:46 +0000 Received: by mail.kernel.org (Postfix) with ESMTPSA id 7FC0D61076; Wed, 23 Jun 2021 07:27:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1624433264; bh=MfGpAhkgNAsV4Gs6J3HXShXQ6oCjPOD50RyhMvI5TIg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=VL3P8zhD1J20JIY2+okRVn52pWiyX0awT2ZEVB1iqKyPEBYhY9PaQjYqUQzPkriup d9d1+2/QNqASXUYg+5eheF++kEPxPVMbHSwrOsoBQbv/e3FSK+pudi4Plpyu9fxbpe GV+0b11T757IsJ8cMWyS/7IkjBHHTatjN+TCeVsw= Date: Wed, 23 Jun 2021 09:27:41 +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-Disposition: inline In-Reply-To: X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210623_002744_709056_84E5D879 X-CRM114-Status: GOOD ( 37.30 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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. > 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 :( > > 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, greg k-h _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel