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

[Takashi Iwai]

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.slawin...@linux.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;
        }