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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, USER_AGENT_MUTT autolearn=ham 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 3D117C04EB8 for ; Wed, 12 Dec 2018 11:19:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 005512084E for ; Wed, 12 Dec 2018 11:19:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1544613592; bh=QKa5zYsHxYI1aGgEq7tsjj3bty4Nm9iYE05hv42O6e4=; h=Date:From:To:Subject:References:In-Reply-To:List-ID:From; b=tUS/ykvUwcrFeabgpsbZJw2T7uYKBY8LZH6pcCu9YMls9ZOMUS5MzqxCRfFfN5JQr sTTi0uEC9ZyWi70U2kcRU4gQgIIyET+Szw0Q5k0ksA9k9tucXF426z6+wAvCRshwao QssDnWJCDUWfsON6EDlRterKbPjjmhTUE2xgFEJs= DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 005512084E Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727262AbeLLLTu (ORCPT ); Wed, 12 Dec 2018 06:19:50 -0500 Received: from mail.kernel.org ([198.145.29.99]:45866 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726856AbeLLLTu (ORCPT ); Wed, 12 Dec 2018 06:19:50 -0500 Received: from localhost (5356596B.cm-6-7b.dynamic.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 413B42084E; Wed, 12 Dec 2018 11:19:49 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1544613589; bh=QKa5zYsHxYI1aGgEq7tsjj3bty4Nm9iYE05hv42O6e4=; h=Date:From:To:Subject:References:In-Reply-To:From; b=Cl2Q80dXbOcBc+Df03jR+jtq9eWnLR1q5QYzbJ2n+3zl3onRFKOMHDEgye5GJSKDU YMjJQ7PShVMnAbp2wvPUoK+yO8fdkdVFbw/4k4WzlJIWwS/Dwo6x4fSxHMhKTkYK4j d9xsJwUZFo5ZU1cAwqrPdfluDOrTlb43iOBHRQtY= Date: Wed, 12 Dec 2018 12:19:47 +0100 From: Greg Kroah-Hartman To: LKML , DRI Development , Ramalingam C , "Rafael J. Wysocki" , Daniel Vetter Subject: Re: [PATCH] drivers/base: use a worker for sysfs unbind Message-ID: <20181212111947.GA12685@kroah.com> References: <20181210084653.7268-1-daniel.vetter@ffwll.ch> <20181210100634.GA8836@kroah.com> <20181210101832.GN21184@phenom.ffwll.local> <20181210102058.GO21184@phenom.ffwll.local> <20181212110840.GA21184@phenom.ffwll.local> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20181212110840.GA21184@phenom.ffwll.local> User-Agent: Mutt/1.11.1 (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Dec 12, 2018 at 12:08:40PM +0100, Daniel Vetter wrote: > On Mon, Dec 10, 2018 at 11:20:58AM +0100, Daniel Vetter wrote: > > On Mon, Dec 10, 2018 at 11:18:32AM +0100, Daniel Vetter wrote: > > > On Mon, Dec 10, 2018 at 11:06:34AM +0100, Greg Kroah-Hartman wrote: > > > > On Mon, Dec 10, 2018 at 09:46:53AM +0100, Daniel Vetter wrote: > > > > > Drivers might want to remove some sysfs files, which needs the same > > > > > locks and ends up angering lockdep. Relevant snippet of the stack > > > > > trace: > > > > > > > > > > kernfs_remove_by_name_ns+0x3b/0x80 > > > > > bus_remove_driver+0x92/0xa0 > > > > > acpi_video_unregister+0x24/0x40 > > > > > i915_driver_unload+0x42/0x130 [i915] > > > > > i915_pci_remove+0x19/0x30 [i915] > > > > > pci_device_remove+0x36/0xb0 > > > > > device_release_driver_internal+0x185/0x250 > > > > > unbind_store+0xaf/0x180 > > > > > kernfs_fop_write+0x104/0x190 > > > > > > > > > > I've stumbled over this because some new patches by Ram connect the > > > > > snd-hda-intel unload (where we do use sysfs unbind) with the locking > > > > > chains in the i915 unload code (but without creating a new loop), > > > > > which upset our CI. But the bug is already there and can be easily > > > > > reproduced by unbind i915 directly. > > > > > > > > This is odd, why wouldn't any driver hit this issue? And why now since > > > > you say this is triggerable today? > > > > > > The above backtrace is triggered by unbinding i915 on current upstream > > > kernels. Note: Will crash later on rather badly in the > > > fbdev/fbcon/vtconsole hell, but that's separate issue (which can be worked > > > around by first unbinding fbcon manually through sysfs). > > > > > > > I know scsi was doing some strange things like trying to remove the > > > > device itself from a sysfs callback on the device, which requires it to > > > > just call a different kobject function created just for that type of > > > > thing. Would that also make sense to do here instead of your workqueue? > > > > > > Note how we blow up on unregistering sw device instances supported by i915 > > > in entirely different subsystems. I guess most drivers just have sysfs > > > files for their own stuff, where this is done as you describe. The problem > > > is that there's an awful lot of unrelated stuff hanging off i915. > > > > > > Or maybe acpi_video is busted, and should be using a different function. > > > You haven't said which one, and I have no idea which one it is ... > > > > > > And in case the context wasn't clear: This is unbinding the i915 pci > > > driver which triggers the above lockdep splat recursion. > > > > btw another option for "fixing" this would be to annotate the mutex_lock > > in kernfs_remove_by_name_ns as recursive. Which just shuts up lockdep (and > > might hide some real bugs), but would get the job done since there's not > > actually a deadlock here. Just lockdep being annoyed. > > So what's the pick? I can do the typing, but I don't understand all the > driver core interactions to know what we should be doing here best. Sorry for the delay. Look at sdev_store_delete() in drivers/scsi/scsi_sysfs.c and see if the logic there makes sense to do here instead. It still seems odd that removing a sysfs file by writing to a sysfs file at the same level really invokes lockdep as I would have thought that this path is well-tested by now. thanks, greg k-h