[PATCH AUTOSEL 6.11 099/244] ALSA: control: Take power_ref lock primarily

Sasha Levin
2024-09-25T11:41:25Z

From: Takashi Iwai <tiwai@suse.de>

[ Upstream commit fcc62b19104a67b9a2941513771e09389b75bd95 ]

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: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
sound/core/control.c | 54 ++++++++++++++++++++++++++++----------------
1 file changed, 34 insertions(+), 20 deletions(-)

diff --git a/sound/core/control.c b/sound/core/control.c
index f64a555f404f0..96a2c088a460e 100644
--- a/sound/core/control.c
+++ b/sound/core/control.c
@@ -1167,9 +1167,7 @@ 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);
+ result = kctl->info(kctl, info);
snd_power_unref(card);
if (result >= 0) {
snd_BUG_ON(info->access);
@@ -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);
+ ret = kctl->get(kctl, control);
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;
--
2.43.0