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=-7.2 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED 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 C3831C43387 for ; Tue, 18 Dec 2018 21:40:51 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7E9BB218A4 for ; Tue, 18 Dec 2018 21:40:51 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1545169251; bh=pUOYrr9MPMPIplizYxf3hlbSzc/vgk9BddWeuUtBEG4=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=oHJysX17kB1BU8gTu4raVNezyA2vTcGt00atluz1y6Bvw8naALXVw3hGw/p33BH7s ENbJgQnBa+jRuwc7gE01S8cMmFqL9NUOpGHm0jmWeUump8McURUjimq6c3r+KNviL9 EQUY6UDzFeXB0dPJXRm++7GauuOg3kqy+W/Ux9DM= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727367AbeLRVku (ORCPT ); Tue, 18 Dec 2018 16:40:50 -0500 Received: from mail-oi1-f194.google.com ([209.85.167.194]:45793 "EHLO mail-oi1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726675AbeLRVkt (ORCPT ); Tue, 18 Dec 2018 16:40:49 -0500 Received: by mail-oi1-f194.google.com with SMTP id y1so3195142oie.12 for ; Tue, 18 Dec 2018 13:40:48 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=IIXaUUd3iN6SGQAMtcDUUcvX+a/mGjDT/KJH5i6GVQQ=; b=N+vvZ5zTJtmJ81mysi83aHqoG3dVTvvr9xTiBqEdkRnJSxZK4QJJFb0Y8meqmldZEc sakkclTtphPvch+KS8tw3BUV1+EKkk/EMUJk2rQSb68nOHbZdDDYBh4e3zLCH9wNK8/N l8WWbeOs1UqwO18ixnSzgmNFbkiRzsaJkCxpcwTVQN/pIAal59uKnvAx16vcltCUdgdY qS2uPFmr+pupa5/IR+sAL4G9aIK6jXo4bpCTSkl9MxIvLfhoFugq7gGZQoOy9+DhcFq6 tuilOnNGnkXVyzgSehLhFEPzMfXyfCxaC4OeDtjkns0F33Td8x6cplcrDuG0DPXwZSFZ l3OQ== X-Gm-Message-State: AA+aEWb9qDAnVdk7Yn0U3WpP32qIVXM3MhDQ+X+h7uF+1JWYMm29JfMq W0KwJEoVciFDrNAFCgXs94BmdsNJ+yjqNX8UrHF5PQ== X-Google-Smtp-Source: AFSGD/UkXOl9KbvEIESVvZFhcEngqgFQwcYHhsoZ9LVlJG5P7h1j9Uy3F5tpxWgyVTiWjxUjGHRryfWJyEXSrjVQysc= X-Received: by 2002:aca:368a:: with SMTP id d132mr9219603oia.193.1545169248272; Tue, 18 Dec 2018 13:40:48 -0800 (PST) MIME-Version: 1.0 References: <20181218201443.4950-1-daniel.vetter@ffwll.ch> In-Reply-To: <20181218201443.4950-1-daniel.vetter@ffwll.ch> From: "Rafael J. Wysocki" Date: Tue, 18 Dec 2018 22:40:37 +0100 Message-ID: Subject: Re: [PATCH] sysfs: Disable lockdep for driver bind/unbind files To: Daniel Vetter Cc: dri-devel , intel-gfx , Linux Kernel Mailing List , "Rafael J. Wysocki" , Greg Kroah-Hartman , ramalingam.c@intel.com, aspriel@gmail.com, Andy Shevchenko , Geert Uytterhoeven , brgl@bgdev.pl, Heikki Krogerus , Vivek Gautam , Joe Perches , Daniel Vetter Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 18, 2018 at 9:14 PM Daniel Vetter wrote: > > This is the much more correct fix for my earlier attempt at: > > https://lkml.org/lkml/2018/12/10/118 > > Short recap: > > - There's not actually a locking issue, it's just lockdep being a bit > too eager to complain about a possible deadlock. > > - Contrary to what I claimed the real problem is recursion on > kn->count. Greg pointed me at sysfs_break_active_protection(), used > by the scsi subsystem to allow a sysfs file to unbind itself. That > would be a real deadlock, which isn't what's happening here. Also, > breaking the active protection means we'd need to manually handle > all the lifetime fun. > > - With Rafael we discussed the task_work approach, which kinda works, > but has two downsides: It's a functional change for a lockdep > annotation issue, and it won't work for the bind file (which needs > to get the errno from the driver load function back to userspace). > > - Greg also asked why this never showed up: To hit this you need to > unregister a 2nd driver from the unload code of your first driver. I > guess only gpus do that. The bug has always been there, but only > with a recent patch series did we add more locks so that lockdep > built a chain from unbinding the snd-hda driver to the > acpi_video_unregister call. > > Full lockdep splat: > > [12301.898799] ============================================ > [12301.898805] WARNING: possible recursive locking detected > [12301.898811] 4.20.0-rc7+ #84 Not tainted > [12301.898815] -------------------------------------------- > [12301.898821] bash/5297 is trying to acquire lock: > [12301.898826] 00000000f61c6093 (kn->count#39){++++}, at: kernfs_remove_by_name_ns+0x3b/0x80 > [12301.898841] but task is already holding lock: > [12301.898847] 000000005f634021 (kn->count#39){++++}, at: kernfs_fop_write+0xdc/0x190 > [12301.898856] other info that might help us debug this: > [12301.898862] Possible unsafe locking scenario: > [12301.898867] CPU0 > [12301.898870] ---- > [12301.898874] lock(kn->count#39); > [12301.898879] lock(kn->count#39); > [12301.898883] *** DEADLOCK *** > [12301.898891] May be due to missing lock nesting notation > [12301.898899] 5 locks held by bash/5297: > [12301.898903] #0: 00000000cd800e54 (sb_writers#4){.+.+}, at: vfs_write+0x17f/0x1b0 > [12301.898915] #1: 000000000465e7c2 (&of->mutex){+.+.}, at: kernfs_fop_write+0xd3/0x190 > [12301.898925] #2: 000000005f634021 (kn->count#39){++++}, at: kernfs_fop_write+0xdc/0x190 > [12301.898936] #3: 00000000414ef7ac (&dev->mutex){....}, at: device_release_driver_internal+0x34/0x240 > [12301.898950] #4: 000000003218fbdf (register_count_mutex){+.+.}, at: acpi_video_unregister+0xe/0x40 > [12301.898960] stack backtrace: > [12301.898968] CPU: 1 PID: 5297 Comm: bash Not tainted 4.20.0-rc7+ #84 > [12301.898974] Hardware name: Hewlett-Packard HP EliteBook 8460p/161C, BIOS 68SCF Ver. F.01 03/11/2011 > [12301.898982] Call Trace: > [12301.898989] dump_stack+0x67/0x9b > [12301.898997] __lock_acquire+0x6ad/0x1410 > [12301.899003] ? kernfs_remove_by_name_ns+0x3b/0x80 > [12301.899010] ? find_held_lock+0x2d/0x90 > [12301.899017] ? mutex_spin_on_owner+0xe4/0x150 > [12301.899023] ? find_held_lock+0x2d/0x90 > [12301.899030] ? lock_acquire+0x90/0x180 > [12301.899036] lock_acquire+0x90/0x180 > [12301.899042] ? kernfs_remove_by_name_ns+0x3b/0x80 > [12301.899049] __kernfs_remove+0x296/0x310 > [12301.899055] ? kernfs_remove_by_name_ns+0x3b/0x80 > [12301.899060] ? kernfs_name_hash+0xd/0x80 > [12301.899066] ? kernfs_find_ns+0x6c/0x100 > [12301.899073] kernfs_remove_by_name_ns+0x3b/0x80 > [12301.899080] bus_remove_driver+0x92/0xa0 > [12301.899085] acpi_video_unregister+0x24/0x40 > [12301.899127] i915_driver_unload+0x42/0x130 [i915] > [12301.899160] i915_pci_remove+0x19/0x30 [i915] > [12301.899169] pci_device_remove+0x36/0xb0 > [12301.899176] device_release_driver_internal+0x185/0x240 > [12301.899183] unbind_store+0xaf/0x180 > [12301.899189] kernfs_fop_write+0x104/0x190 > [12301.899195] __vfs_write+0x31/0x180 > [12301.899203] ? rcu_read_lock_sched_held+0x6f/0x80 > [12301.899209] ? rcu_sync_lockdep_assert+0x29/0x50 > [12301.899216] ? __sb_start_write+0x13c/0x1a0 > [12301.899221] ? vfs_write+0x17f/0x1b0 > [12301.899227] vfs_write+0xb9/0x1b0 > [12301.899233] ksys_write+0x50/0xc0 > [12301.899239] do_syscall_64+0x4b/0x180 > [12301.899247] entry_SYSCALL_64_after_hwframe+0x49/0xbe > [12301.899253] RIP: 0033:0x7f452ac7f7a4 > [12301.899259] Code: 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b7 0f 1f 80 00 00 00 00 8b 05 aa f0 2c 00 48 63 ff 85 c0 75 13 b8 01 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 54 f3 c3 66 90 55 53 48 89 d5 48 89 f3 48 83 > [12301.899273] RSP: 002b:00007ffceafa6918 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 > [12301.899282] RAX: ffffffffffffffda RBX: 000000000000000d RCX: 00007f452ac7f7a4 > [12301.899288] RDX: 000000000000000d RSI: 00005612a1abf7c0 RDI: 0000000000000001 > [12301.899295] RBP: 00005612a1abf7c0 R08: 000000000000000a R09: 00005612a1c46730 > [12301.899301] R10: 000000000000000a R11: 0000000000000246 R12: 000000000000000d > [12301.899308] R13: 0000000000000001 R14: 00007f452af4a740 R15: 000000000000000d > > Locking around I've noticed that usb and i2c already handle similar "Looking" I suppose? ;-) Apart from this LGTM, so Reviewed-by: Rafael J. Wysocki > recursion problems, where a sysfs file can unbind the same type of > sysfs somewhere else in the hierarchy. Relevant commits are: > > commit 356c05d58af05d582e634b54b40050c73609617b > Author: Alan Stern > Date: Mon May 14 13:30:03 2012 -0400 > > sysfs: get rid of some lockdep false positives > > commit e9b526fe704812364bca07edd15eadeba163ebfb > Author: Alexander Sverdlin > Date: Fri May 17 14:56:35 2013 +0200 > > i2c: suppress lockdep warning on delete_device > > Implement the same trick for driver bind/unbind. > > Cc: "Rafael J. Wysocki" > Cc: Greg Kroah-Hartman > Cc: Ramalingam C > Cc: Arend van Spriel > Cc: Andy Shevchenko > Cc: Geert Uytterhoeven > Cc: Bartosz Golaszewski > Cc: Heikki Krogerus > Cc: Vivek Gautam > Cc: Joe Perches > Signed-off-by: Daniel Vetter > --- > drivers/base/bus.c | 4 ++-- > include/linux/device.h | 4 ++++ > 2 files changed, 6 insertions(+), 2 deletions(-) > > diff --git a/drivers/base/bus.c b/drivers/base/bus.c > index 8bfd27ec73d6..5d2411b848cd 100644 > --- a/drivers/base/bus.c > +++ b/drivers/base/bus.c > @@ -195,7 +195,7 @@ static ssize_t unbind_store(struct device_driver *drv, const char *buf, > bus_put(bus); > return err; > } > -static DRIVER_ATTR_WO(unbind); > +static DRIVER_ATTR_IGNORE_LOCKDEP(unbind, S_IWUSR, NULL, unbind_store); > > /* > * Manually attach a device to a driver. > @@ -231,7 +231,7 @@ static ssize_t bind_store(struct device_driver *drv, const char *buf, > bus_put(bus); > return err; > } > -static DRIVER_ATTR_WO(bind); > +static DRIVER_ATTR_IGNORE_LOCKDEP(bind, S_IWUSR, NULL, bind_store); > > static ssize_t show_drivers_autoprobe(struct bus_type *bus, char *buf) > { > diff --git a/include/linux/device.h b/include/linux/device.h > index 1b25c7a43f4c..d2cb1a6c5d95 100644 > --- a/include/linux/device.h > +++ b/include/linux/device.h > @@ -326,6 +326,10 @@ struct driver_attribute { > struct driver_attribute driver_attr_##_name = __ATTR_RO(_name) > #define DRIVER_ATTR_WO(_name) \ > struct driver_attribute driver_attr_##_name = __ATTR_WO(_name) > +#define DRIVER_ATTR_IGNORE_LOCKDEP(_name, _mode, _show, _store) \ > + struct driver_attribute driver_attr_##_name = \ > + __ATTR_IGNORE_LOCKDEP(_name, _mode, _show, _store) > + > > extern int __must_check driver_create_file(struct device_driver *driver, > const struct driver_attribute *attr); > -- > 2.20.0.rc1 >