linux-kernel - Re: [PATCH] ALSA: hda: Fix race between creating and refreshing sysfs entries

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Date:   Fri, 10 May 2019 14:33:53 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Amadeusz Sławiński 
        <amadeuszx.slawinski@...ux.intel.com>
Cc:     <alsa-devel@...a-project.org>, "Jaroslav Kysela" <perex@...ex.cz>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ALSA: hda: Fix race between creating and refreshing sysfs entries

On Fri, 10 May 2019 14:21:41 +0200,
Amadeusz Sławiński wrote:
> 
> hda_widget_sysfs_reinit() can free underlying codec->widgets structure
> on which widget_tree_create() operates. Add locking to prevent such
> issues from happening.
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=110382
> Signed-off-by: Amadeusz Sławiński <amadeuszx.slawinski@...ux.intel.com>

Thanks, the idea looks good.  But it'd be simpler to do mutex
lock/unlock in the caller side, a patch like below.


Takashi

--- a/include/sound/hdaudio.h
+++ b/include/sound/hdaudio.h
@@ -81,6 +81,7 @@ struct hdac_device {
 	atomic_t in_pm;		/* suspend/resume being performed */
 
 	/* sysfs */
+	struct mutex widget_lock;
 	struct hdac_widget_tree *widgets;
 
 	/* regmap */
--- a/sound/hda/hdac_device.c
+++ b/sound/hda/hdac_device.c
@@ -55,6 +55,7 @@ int snd_hdac_device_init(struct hdac_device *codec, struct hdac_bus *bus,
 	codec->bus = bus;
 	codec->addr = addr;
 	codec->type = HDA_DEV_CORE;
+	mutex_init(&codec->widget_lock);
 	pm_runtime_set_active(&codec->dev);
 	pm_runtime_get_noresume(&codec->dev);
 	atomic_set(&codec->in_pm, 0);
@@ -141,7 +142,9 @@ int snd_hdac_device_register(struct hdac_device *codec)
 	err = device_add(&codec->dev);
 	if (err < 0)
 		return err;
+	mutex_lock(&codec->widget_lock);
 	err = hda_widget_sysfs_init(codec);
+	mutex_unlock(&codec->widget_lock);
 	if (err < 0) {
 		device_del(&codec->dev);
 		return err;
@@ -158,7 +161,9 @@ EXPORT_SYMBOL_GPL(snd_hdac_device_register);
 void snd_hdac_device_unregister(struct hdac_device *codec)
 {
 	if (device_is_registered(&codec->dev)) {
+		mutex_lock(&codec->widget_lock);
 		hda_widget_sysfs_exit(codec);
+		mutex_unlock(&codec->widget_lock);
 		device_del(&codec->dev);
 		snd_hdac_bus_remove_device(codec->bus, codec);
 	}
@@ -404,7 +409,9 @@ int snd_hdac_refresh_widgets(struct hdac_device *codec, bool sysfs)
 	}
 
 	if (sysfs) {
+		mutex_lock(&codec->widget_lock);
 		err = hda_widget_sysfs_reinit(codec, start_nid, nums);
+		mutex_unlock(&codec->widget_lock);
 		if (err < 0)
 			return err;
 	}