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 1E2DBC433ED for ; Tue, 27 Apr 2021 12:41:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D4B3261073 for ; Tue, 27 Apr 2021 12:41:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236139AbhD0MmB (ORCPT ); Tue, 27 Apr 2021 08:42:01 -0400 Received: from mail.kernel.org ([198.145.29.99]:55624 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235410AbhD0MmA (ORCPT ); Tue, 27 Apr 2021 08:42:00 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 457B861059; Tue, 27 Apr 2021 12:41:17 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1619527277; bh=P+oLcg/KgUKwLIvYmcCRqckymcvWUs4EWrMcpfr89qA=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Si+4HW3ASVsCkRRhUXpnUKiBsIwvgH3s6gMg4zAZtzXEBMAmchfr006GslZOmi5ne zmyRrYlPnFg9Gj9jQ+zSQi0qCfjzk2AUWbN6rWwfgbhACVw4/Ibky3v05fZ2wOybUi aCGmRnJQGAhbBdGCJVlGikWmDcmXUoCL4vLwa3EQ= Date: Tue, 27 Apr 2021 14:41:15 +0200 From: Greg KH To: Robin Murphy Cc: Corentin Labbe , rafael@kernel.org, hch@lst.de, m.szyprowski@samsung.com, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org Subject: Re: dma-api debugfs directory is not created since debugfs is not initialized Message-ID: References: <22f268bb-9b96-1208-0292-68c9b50422a1@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <22f268bb-9b96-1208-0292-68c9b50422a1@arm.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Apr 27, 2021 at 01:32:50PM +0100, Robin Murphy wrote: > 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 :/ init call ordering happens from link ordering. > 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. That seems like a better idea here, there's no need for "special treatment" of debugfs. thanks, greg k-h