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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 526F7C433F5 for ; Mon, 15 Nov 2021 22:18:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 31E5960F0F for ; Mon, 15 Nov 2021 22:18:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345177AbhKOWUx (ORCPT ); Mon, 15 Nov 2021 17:20:53 -0500 Received: from mail.kernel.org ([198.145.29.99]:42058 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242237AbhKOSe7 (ORCPT ); Mon, 15 Nov 2021 13:34:59 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id 43BFB63467; Mon, 15 Nov 2021 18:00:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1636999256; bh=TWPmQS2Ni35f8roJ7s3PkAA8b+MgmQhOvGWfB0y7x94=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=dKQUZNdDZFb98KaWQBnZ57v3ILLrNVPE912JE+f9EHq3FEyk+BVzC61qgiH58zzz0 w1pKJB2JtgT/FdyNmMaqutlu880E/XptbBFrngWCOyt2VgmSbWcv1gz9VZq64dzfnC fUEOe90GRwV0vslgzh/uoEbNJzwPR9S6dXpSyD+o= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Johannes Berg , Pavel Machek , Sasha Levin Subject: [PATCH 5.14 232/849] leds: trigger: use RCU to protect the led_cdevs list Date: Mon, 15 Nov 2021 17:55:15 +0100 Message-Id: <20211115165428.044566164@linuxfoundation.org> X-Mailer: git-send-email 2.33.1 In-Reply-To: <20211115165419.961798833@linuxfoundation.org> References: <20211115165419.961798833@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Johannes Berg [ Upstream commit 2a5a8fa8b23144d14567d6f8293dd6fbeecee393 ] Even with the previous commit 27af8e2c90fb ("leds: trigger: fix potential deadlock with libata") to this file, we still get lockdep unhappy, and Boqun explained the report here: https://lore.kernel.org/r/YNA+d1X4UkoQ7g8a@boqun-archlinux Effectively, this means that the read_lock_irqsave() isn't enough here because another CPU might be trying to do a write lock, and thus block the readers. This is all pretty messy, but it doesn't seem right that the LEDs framework imposes some locking requirements on users, in particular we'd have to make the spinlock in the iwlwifi driver always disable IRQs, even if we don't need that for any other reason, just to avoid this deadlock. Since writes to the led_cdevs list are rare (and are done by userspace), just switch the list to RCU. This costs a synchronize_rcu() at removal time so we can ensure things are correct, but that seems like a small price to pay for getting lock-free iterations and no deadlocks (nor any locking requirements imposed on users.) Signed-off-by: Johannes Berg Signed-off-by: Pavel Machek Signed-off-by: Sasha Levin --- drivers/leds/led-triggers.c | 41 +++++++++++++++++++------------------ include/linux/leds.h | 2 +- 2 files changed, 22 insertions(+), 21 deletions(-) diff --git a/drivers/leds/led-triggers.c b/drivers/leds/led-triggers.c index 4e7b78a84149b..072491d3e17b0 100644 --- a/drivers/leds/led-triggers.c +++ b/drivers/leds/led-triggers.c @@ -157,7 +157,6 @@ EXPORT_SYMBOL_GPL(led_trigger_read); /* Caller must ensure led_cdev->trigger_lock held */ int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig) { - unsigned long flags; char *event = NULL; char *envp[2]; const char *name; @@ -171,10 +170,13 @@ int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig) /* Remove any existing trigger */ if (led_cdev->trigger) { - write_lock_irqsave(&led_cdev->trigger->leddev_list_lock, flags); - list_del(&led_cdev->trig_list); - write_unlock_irqrestore(&led_cdev->trigger->leddev_list_lock, - flags); + spin_lock(&led_cdev->trigger->leddev_list_lock); + list_del_rcu(&led_cdev->trig_list); + spin_unlock(&led_cdev->trigger->leddev_list_lock); + + /* ensure it's no longer visible on the led_cdevs list */ + synchronize_rcu(); + cancel_work_sync(&led_cdev->set_brightness_work); led_stop_software_blink(led_cdev); if (led_cdev->trigger->deactivate) @@ -186,9 +188,9 @@ int led_trigger_set(struct led_classdev *led_cdev, struct led_trigger *trig) led_set_brightness(led_cdev, LED_OFF); } if (trig) { - write_lock_irqsave(&trig->leddev_list_lock, flags); - list_add_tail(&led_cdev->trig_list, &trig->led_cdevs); - write_unlock_irqrestore(&trig->leddev_list_lock, flags); + spin_lock(&trig->leddev_list_lock); + list_add_tail_rcu(&led_cdev->trig_list, &trig->led_cdevs); + spin_unlock(&trig->leddev_list_lock); led_cdev->trigger = trig; if (trig->activate) @@ -223,9 +225,10 @@ err_add_groups: trig->deactivate(led_cdev); err_activate: - write_lock_irqsave(&led_cdev->trigger->leddev_list_lock, flags); - list_del(&led_cdev->trig_list); - write_unlock_irqrestore(&led_cdev->trigger->leddev_list_lock, flags); + spin_lock(&led_cdev->trigger->leddev_list_lock); + list_del_rcu(&led_cdev->trig_list); + spin_unlock(&led_cdev->trigger->leddev_list_lock); + synchronize_rcu(); led_cdev->trigger = NULL; led_cdev->trigger_data = NULL; led_set_brightness(led_cdev, LED_OFF); @@ -285,7 +288,7 @@ int led_trigger_register(struct led_trigger *trig) struct led_classdev *led_cdev; struct led_trigger *_trig; - rwlock_init(&trig->leddev_list_lock); + spin_lock_init(&trig->leddev_list_lock); INIT_LIST_HEAD(&trig->led_cdevs); down_write(&triggers_list_lock); @@ -378,15 +381,14 @@ void led_trigger_event(struct led_trigger *trig, enum led_brightness brightness) { struct led_classdev *led_cdev; - unsigned long flags; if (!trig) return; - read_lock_irqsave(&trig->leddev_list_lock, flags); - list_for_each_entry(led_cdev, &trig->led_cdevs, trig_list) + rcu_read_lock(); + list_for_each_entry_rcu(led_cdev, &trig->led_cdevs, trig_list) led_set_brightness(led_cdev, brightness); - read_unlock_irqrestore(&trig->leddev_list_lock, flags); + rcu_read_unlock(); } EXPORT_SYMBOL_GPL(led_trigger_event); @@ -397,20 +399,19 @@ static void led_trigger_blink_setup(struct led_trigger *trig, int invert) { struct led_classdev *led_cdev; - unsigned long flags; if (!trig) return; - read_lock_irqsave(&trig->leddev_list_lock, flags); - list_for_each_entry(led_cdev, &trig->led_cdevs, trig_list) { + rcu_read_lock(); + list_for_each_entry_rcu(led_cdev, &trig->led_cdevs, trig_list) { if (oneshot) led_blink_set_oneshot(led_cdev, delay_on, delay_off, invert); else led_blink_set(led_cdev, delay_on, delay_off); } - read_unlock_irqrestore(&trig->leddev_list_lock, flags); + rcu_read_unlock(); } void led_trigger_blink(struct led_trigger *trig, diff --git a/include/linux/leds.h b/include/linux/leds.h index 329fd914cf243..fa59326b0ad9f 100644 --- a/include/linux/leds.h +++ b/include/linux/leds.h @@ -354,7 +354,7 @@ struct led_trigger { struct led_hw_trigger_type *trigger_type; /* LEDs under control by this trigger (for simple triggers) */ - rwlock_t leddev_list_lock; + spinlock_t leddev_list_lock; struct list_head led_cdevs; /* Link to next registered trigger */ -- 2.33.0