Commit fcc62b19 authored by Takashi Iwai's avatar Takashi Iwai
Browse files

ALSA: control: Take power_ref lock primarily 

The code path for kcontrol accesses have often nested locks of both
card's controls_rwsem and power_ref, and applies in that order.
However, what could take much longer is the latter, power_ref; it
waits for the power state of the device, and it pretty much depends on
the user's action.

This patch swaps the locking order of those locks to a more natural
way, namely, power_ref -> controls_rwsem, in order to shorten the time
of possible nested locks.  For consistency, power_ref is taken always
in the top-level caller side (that is, *_user() functions and the
ioctl handler itself).

Link: https://patch.msgid.link/20240729160659.4516-1-tiwai@suse.de


Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>
parent 3bb66826

sound/core/control.c

+34 −20
Original line number Diff line number Diff line
@@ -1167,8 +1167,6 @@ static int __snd_ctl_elem_info(struct snd_card *card, 
#ifdef CONFIG_SND_DEBUG

	info->access = 0;

#endif

	result = snd_power_ref_and_wait(card);

	if (!result)

	result = kctl->info(kctl, info);

	snd_power_unref(card);

	if (result >= 0) {
@@ -1208,12 +1206,17 @@ static int snd_ctl_elem_info(struct snd_ctl_file *ctl, 
static int snd_ctl_elem_info_user(struct snd_ctl_file *ctl,

				  struct snd_ctl_elem_info __user *_info)

{

	struct snd_card *card = ctl->card;

	struct snd_ctl_elem_info info;

	int result;



	if (copy_from_user(&info, _info, sizeof(info)))

		return -EFAULT;

	result = snd_power_ref_and_wait(card);

	if (result)

		return result;

	result = snd_ctl_elem_info(ctl, &info);

	snd_power_unref(card);

	if (result < 0)

		return result;

	/* drop internal access flags */
@@ -1257,10 +1260,7 @@ static int snd_ctl_elem_read(struct snd_card *card, 


	if (!snd_ctl_skip_validation(&info))

		fill_remaining_elem_value(control, &info, pattern);

	ret = snd_power_ref_and_wait(card);

	if (!ret)

	ret = kctl->get(kctl, control);

	snd_power_unref(card);

	if (ret < 0)

		return ret;

	if (!snd_ctl_skip_validation(&info) &&
@@ -1285,7 +1285,11 @@ static int snd_ctl_elem_read_user(struct snd_card *card, 
	if (IS_ERR(control))

		return PTR_ERR(no_free_ptr(control));



	result = snd_power_ref_and_wait(card);

	if (result)

		return result;

	result = snd_ctl_elem_read(card, control);

	snd_power_unref(card);

	if (result < 0)

		return result;
@@ -1300,7 +1304,7 @@ static int snd_ctl_elem_write(struct snd_card *card, struct snd_ctl_file *file, 
	struct snd_kcontrol *kctl;

	struct snd_kcontrol_volatile *vd;

	unsigned int index_offset;

	int result;

	int result = 0;



	down_write(&card->controls_rwsem);

	kctl = snd_ctl_find_id_locked(card, &control->id);
@@ -1318,9 +1322,8 @@ static int snd_ctl_elem_write(struct snd_card *card, struct snd_ctl_file *file, 
	}



	snd_ctl_build_ioff(&control->id, kctl, index_offset);

	result = snd_power_ref_and_wait(card);

	/* validate input values */

	if (IS_ENABLED(CONFIG_SND_CTL_INPUT_VALIDATION) && !result) {

	if (IS_ENABLED(CONFIG_SND_CTL_INPUT_VALIDATION)) {

		struct snd_ctl_elem_info info;



		memset(&info, 0, sizeof(info));
@@ -1332,7 +1335,6 @@ static int snd_ctl_elem_write(struct snd_card *card, struct snd_ctl_file *file, 
	}

	if (!result)

		result = kctl->put(kctl, control);

	snd_power_unref(card);

	if (result < 0) {

		up_write(&card->controls_rwsem);

		return result;
@@ -1361,7 +1363,11 @@ static int snd_ctl_elem_write_user(struct snd_ctl_file *file, 
		return PTR_ERR(no_free_ptr(control));



	card = file->card;

	result = snd_power_ref_and_wait(card);

	if (result < 0)

		return result;

	result = snd_ctl_elem_write(card, file, control);

	snd_power_unref(card);

	if (result < 0)

		return result;
@@ -1830,7 +1836,7 @@ static int call_tlv_handler(struct snd_ctl_file *file, int op_flag, 
		{SNDRV_CTL_TLV_OP_CMD,   SNDRV_CTL_ELEM_ACCESS_TLV_COMMAND},

	};

	struct snd_kcontrol_volatile *vd = &kctl->vd[snd_ctl_get_ioff(kctl, id)];

	int i, ret;

	int i;



	/* Check support of the request for this element. */

	for (i = 0; i < ARRAY_SIZE(pairs); ++i) {
@@ -1848,11 +1854,7 @@ static int call_tlv_handler(struct snd_ctl_file *file, int op_flag, 
	    vd->owner != NULL && vd->owner != file)

		return -EPERM;



	ret = snd_power_ref_and_wait(file->card);

	if (!ret)

		ret = kctl->tlv.c(kctl, op_flag, size, buf);

	snd_power_unref(file->card);

	return ret;

	return kctl->tlv.c(kctl, op_flag, size, buf);

}



static int read_tlv_buf(struct snd_kcontrol *kctl, struct snd_ctl_elem_id *id,
@@ -1965,16 +1967,28 @@ static long snd_ctl_ioctl(struct file *file, unsigned int cmd, unsigned long arg 
	case SNDRV_CTL_IOCTL_SUBSCRIBE_EVENTS:

		return snd_ctl_subscribe_events(ctl, ip);

	case SNDRV_CTL_IOCTL_TLV_READ:

		scoped_guard(rwsem_read, &ctl->card->controls_rwsem)

		err = snd_power_ref_and_wait(card);

		if (err < 0)

			return err;

		scoped_guard(rwsem_read, &card->controls_rwsem)

			err = snd_ctl_tlv_ioctl(ctl, argp, SNDRV_CTL_TLV_OP_READ);

		snd_power_unref(card);

		return err;

	case SNDRV_CTL_IOCTL_TLV_WRITE:

		scoped_guard(rwsem_write, &ctl->card->controls_rwsem)

		err = snd_power_ref_and_wait(card);

		if (err < 0)

			return err;

		scoped_guard(rwsem_write, &card->controls_rwsem)

			err = snd_ctl_tlv_ioctl(ctl, argp, SNDRV_CTL_TLV_OP_WRITE);

		snd_power_unref(card);

		return err;

	case SNDRV_CTL_IOCTL_TLV_COMMAND:

		scoped_guard(rwsem_write, &ctl->card->controls_rwsem)

		err = snd_power_ref_and_wait(card);

		if (err < 0)

			return err;

		scoped_guard(rwsem_write, &card->controls_rwsem)

			err = snd_ctl_tlv_ioctl(ctl, argp, SNDRV_CTL_TLV_OP_CMD);

		snd_power_unref(card);

		return err;

	case SNDRV_CTL_IOCTL_POWER:

		return -ENOPROTOOPT;