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, 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 07A2CC433ED for ; Tue, 27 Apr 2021 12:32:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CE7CA60FDB for ; Tue, 27 Apr 2021 12:32:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235951AbhD0Mdk (ORCPT ); Tue, 27 Apr 2021 08:33:40 -0400 Received: from foss.arm.com ([217.140.110.172]:52338 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235410AbhD0Mdj (ORCPT ); Tue, 27 Apr 2021 08:33:39 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A544331B; Tue, 27 Apr 2021 05:32:56 -0700 (PDT) Received: from [10.57.61.101] (unknown [10.57.61.101]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 809803F70D; Tue, 27 Apr 2021 05:32:55 -0700 (PDT) Subject: Re: dma-api debugfs directory is not created since debugfs is not initialized To: Greg KH , Corentin Labbe Cc: rafael@kernel.org, hch@lst.de, m.szyprowski@samsung.com, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org References: From: Robin Murphy Message-ID: <22f268bb-9b96-1208-0292-68c9b50422a1@arm.com> Date: Tue, 27 Apr 2021 13:32:50 +0100 User-Agent: Mozilla/5.0 (Windows NT 10.0; rv:78.0) Gecko/20100101 Thunderbird/78.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2021-04-27 12:39, Greg KH wrote: > On Tue, Apr 27, 2021 at 01:34:27PM +0200, Corentin Labbe wrote: >> Hello >> >> I try to debug some DMA problem on next-20210427, and so I have enabled CONFIG_DMA_API_DEBUG=y. >> But the dma-api directory does show up in debugfs, but lot of other directory exists in it. > > Does it show up properly in 5.12? > >> After debugging it seems due to commit 56348560d495 ("debugfs: do not attempt to create a new file before the filesystem is initalized") >> Reverting the commit permit to "dma-api" debugfs to be found. (but seems not the right way to fix it). > > We have had some odd start-up ordering issues that the above commit has > caused to show. Given that this commit is now in stable kernels, with > no report of this issue so far, I'm worried that maybe this is a dma > subsystem ordering issue? Both debugfs_init() and dma_debug_init() do run at core_initcall level, and disassembling the vmlinux from my current working tree does indeed suggest that they somehow end up in the wrong relative order: [...] ffff80001160d0c8 <__initcall__kmod_debug__325_918_dma_debug_init1>: ffff80001160d0c8: feb0d528 .word 0xfeb0d528 [...] ffff80001160d108 <__initcall__kmod_debugfs__357_848_debugfs_init1>: ffff80001160d108: fff4326c .word 0xfff4326c [...] I always had the impression that initcall ordering tended to work out roughly alphabetical, such that entries from fs/* might come before kernel/*, but I guess it's at the whims of the linker in the end :/ Perhaps the easiest thing to do is split out dma_debug_fs_init() and run that at a later level? We do want the dma-debug infrastructure itself to be up as early as possible, but I think the debugfs view of its internals can happily wait until closer to the time that there's actually a userspace to be able to look at it. Robin.