From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1032945AbeEXUUo (ORCPT ); Thu, 24 May 2018 16:20:44 -0400 Received: from mail-wr0-f196.google.com ([209.85.128.196]:40623 "EHLO mail-wr0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1032690AbeEXUUm (ORCPT ); Thu, 24 May 2018 16:20:42 -0400 X-Google-Smtp-Source: AB8JxZpGJ+CSpm2Hg+HoASWYWTCt8RDLxPzulyEXkBpy+NcdWIdJXwiQiXhT0zNALXS2ilXZRK8W0g== Subject: Re: [PATCH] leds: class: ensure workqueue is initialized before setting brightness To: Luis Henriques , Pavel Machek Cc: linux-leds@vger.kernel.org, linux-kernel@vger.kernel.org References: <20180523222221.27621-1-lhenriques@suse.com> From: Jacek Anaszewski Message-ID: <980e565f-a4da-eaad-0550-fe86a34182ce@gmail.com> Date: Thu, 24 May 2018 22:19:26 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.7.0 MIME-Version: 1.0 In-Reply-To: <20180523222221.27621-1-lhenriques@suse.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Luis, Thank you for the patch. On 05/24/2018 12:22 AM, Luis Henriques wrote: > An application can try to set brightness before all the initialization is > done, in particular before the workqueue is initialized with the call to > led_init_core(). Here's a WARNING easy to trigger: > > [ 36.780813] WARNING: CPU: 3 PID: 1411 at ../kernel/workqueue.c:1444 __queue_work+0x37b/0x420 > [ 36.780815] Modules linked in: ... > [ 36.780868] CPU: 3 PID: 1411 Comm: systemd-backlig Not tainted 4.16.9-1-default #1 openSUSE Tumbleweed (unreleased) > [ 36.780868] Hardware name: Dell Inc. Precision 5510/0N8J4R, BIOS 1.6.1 12/11/2017 > [ 36.780870] RIP: 0010:__queue_work+0x37b/0x420 > [ 36.780871] RSP: 0018:ffffaced048b7d78 EFLAGS: 00010086 > [ 36.780873] RAX: 0000000000000000 RBX: ffffffffb3f01440 RCX: 0000000000000000 > [ 36.780873] RDX: ffffffffc05a90d8 RSI: 0000000000000000 RDI: ffff8eac7dce2700 > [ 36.780874] RBP: ffff8ea547c16400 R08: ffff8ea547800000 R09: ffff8eac7dc22700 > [ 36.780875] R10: 0000000000000000 R11: 0000000000000040 R12: 0000000000000003 > [ 36.780876] R13: 0000000000000200 R14: ffffffffc05a90d0 R15: ffff8eac7dce8600 > [ 36.780877] FS: 00007f871e61cf40(0000) GS:ffff8eac7dcc0000(0000) knlGS:0000000000000000 > [ 36.780878] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 36.780879] CR2: 000055c91115e308 CR3: 0000000883ee0005 CR4: 00000000003606e0 > [ 36.780880] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > [ 36.780880] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > [ 36.780881] Call Trace: > [ 36.780886] queue_work_on+0x81/0x90 > [ 36.780889] brightness_store+0x5d/0x90 > [ 36.780892] kernfs_fop_write+0x105/0x180 > [ 36.780894] __vfs_write+0x26/0x150 > [ 36.780897] ? common_file_perm+0x51/0x150 > [ 36.780900] ? security_file_permission+0x3c/0xb0 > [ 36.780901] vfs_write+0xad/0x1a0 > [ 36.780903] SyS_write+0x42/0x90 > [ 36.780906] do_syscall_64+0x76/0x140 > [ 36.780908] entry_SYSCALL_64_after_hwframe+0x42/0xb7 > [ 36.780910] RIP: 0033:0x7f871dd04c94 > [ 36.780910] RSP: 002b:00007ffeb3a57d38 EFLAGS: 00000246 ORIG_RAX: 0000000000000001 > [ 36.780912] RAX: ffffffffffffffda RBX: 000055c91115c810 RCX: 00007f871dd04c94 > [ 36.780912] RDX: 0000000000000001 RSI: 000055c91115c810 RDI: 0000000000000004 > [ 36.780913] RBP: 00007ffeb3a57e10 R08: 0000000000000003 R09: 0000000000000000 > [ 36.780914] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001 > [ 36.780914] R13: 000055c911158f30 R14: 000055c90f3a9a4e R15: 0000000000000004 > [ 36.780917] Code: 74 18 e8 49 80 00 00 48 85 c0 74 0e 48 8b 40 20 48 3b 68 08 > 0f 84 c2 fc ff ff 0f 0b 48 83 c4 10 5b 5d 41 5c 41 5d 41 5e 41 5f c3 <0f> 0b e9 > 82 fd ff ff 83 cd 02 49 8d 57 60 e9 69 fd ff ff 80 3d > [ 36.780942] ---[ end trace 1fce4edad54c4017 ]--- > > This patch initializes and acquires the led_access mutex early in the > of_led_classdev_register function, so that any application trying to write > to sysfs to set brightness will block until initialization ends. > > Signed-off-by: Luis Henriques > --- > drivers/leds/led-class.c | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-) > > diff --git a/drivers/leds/led-class.c b/drivers/leds/led-class.c > index b0e2d55acbd6..3c7e3487b373 100644 > --- a/drivers/leds/led-class.c > +++ b/drivers/leds/led-class.c > @@ -260,10 +260,14 @@ int of_led_classdev_register(struct device *parent, struct device_node *np, > if (ret < 0) > return ret; > > + mutex_init(&led_cdev->led_access); > + mutex_lock(&led_cdev->led_access); > led_cdev->dev = device_create_with_groups(leds_class, parent, 0, > led_cdev, led_cdev->groups, "%s", name); > - if (IS_ERR(led_cdev->dev)) > + if (IS_ERR(led_cdev->dev)) { > + mutex_unlock(&led_cdev->led_access); > return PTR_ERR(led_cdev->dev); > + } > led_cdev->dev->of_node = np; > > if (ret) > @@ -274,6 +278,7 @@ int of_led_classdev_register(struct device *parent, struct device_node *np, > ret = led_add_brightness_hw_changed(led_cdev); > if (ret) { > device_unregister(led_cdev->dev); > + mutex_unlock(&led_cdev->led_access); > return ret; > } > } > @@ -285,7 +290,6 @@ int of_led_classdev_register(struct device *parent, struct device_node *np, > #ifdef CONFIG_LEDS_BRIGHTNESS_HW_CHANGED > led_cdev->brightness_hw_changed = -1; > #endif > - mutex_init(&led_cdev->led_access); > /* add to the list of leds */ > down_write(&leds_list_lock); > list_add_tail(&led_cdev->node, &leds_list); > @@ -302,6 +306,8 @@ int of_led_classdev_register(struct device *parent, struct device_node *np, > led_trigger_set_default(led_cdev); > #endif > > + mutex_unlock(&led_cdev->led_access); > + > dev_dbg(parent, "Registered led device: %s\n", > led_cdev->name); > > Applied. -- Best regards, Jacek Anaszewski