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ALSA: control: code refactoring for ELEM_READ/ELEM_WRITE operations
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ALSA control core handles ELEM_READ/ELEM_WRITE requests within lock
acquisition of a counting semaphore. The lock is acquired in helper
functions in the end of call path before calling implementations of each
driver.

ioctl(2) with SNDRV_CTL_ELEM_READ
...
->snd_ctl_ioctl()
  ->snd_ctl_elem_read_user()
    ->snd_ctl_elem_read()
      ->down_read(controls_rwsem)
      ->snd_ctl_find_id()
      ->struct snd_kcontrol.get()
      ->up_read(controls_rwsem)

ioctl(2) with SNDRV_CTL_ELEM_WRITE
...
->snd_ctl_ioctl()
  ->snd_ctl_elem_write_user()
    ->snd_ctl_elem_write()
      ->down_read(controls_rwsem)
      ->snd_ctl_find_id()
      ->struct snd_kcontrol.put()
      ->up_read(controls_rwsem)

This commit moves the lock acquisition to middle of the call graph to
simplify the helper functions. As a result:

ioctl(2) with SNDRV_CTL_ELEM_READ
...
->snd_ctl_ioctl()
  ->snd_ctl_elem_read_user()
    ->down_read(controls_rwsem)
    ->snd_ctl_elem_read()
      ->snd_ctl_find_id()
      ->struct snd_kcontrol.get()
    ->up_read(controls_rwsem)

ioctl(2) with SNDRV_CTL_ELEM_WRITE
...
->snd_ctl_ioctl()
  ->snd_ctl_elem_write_user()
    ->down_read(controls_rwsem)
    ->snd_ctl_elem_write()
      ->snd_ctl_find_id()
      ->struct snd_kcontrol.put()
    ->up_read(controls_rwsem)

Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
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@takaswie @tiwai
takaswie authored and tiwai committed Aug 20, 2017
1 parent 7b42cfa commit becf9e5
Showing 1 changed file with 38 additions and 39 deletions.
77 changes: 38 additions & 39 deletions sound/core/control.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -881,24 +881,18 @@ static int snd_ctl_elem_read(struct snd_card *card,
struct snd_kcontrol *kctl;
struct snd_kcontrol_volatile *vd;
unsigned int index_offset;
int result;

down_read(&card->controls_rwsem);
kctl = snd_ctl_find_id(card, &control->id);
if (kctl == NULL) {
result = -ENOENT;
} else {
index_offset = snd_ctl_get_ioff(kctl, &control->id);
vd = &kctl->vd[index_offset];
if ((vd->access & SNDRV_CTL_ELEM_ACCESS_READ) &&
kctl->get != NULL) {
snd_ctl_build_ioff(&control->id, kctl, index_offset);
result = kctl->get(kctl, control);
} else
result = -EPERM;
}
up_read(&card->controls_rwsem);
return result;
if (kctl == NULL)
return -ENOENT;

index_offset = snd_ctl_get_ioff(kctl, &control->id);
vd = &kctl->vd[index_offset];
if (!(vd->access & SNDRV_CTL_ELEM_ACCESS_READ) && kctl->get == NULL)
return -EPERM;

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

static int snd_ctl_elem_read_user(struct snd_card *card,
Expand All @@ -913,8 +907,11 @@ static int snd_ctl_elem_read_user(struct snd_card *card,

snd_power_lock(card);
result = snd_power_wait(card, SNDRV_CTL_POWER_D0);
if (result >= 0)
if (result >= 0) {
down_read(&card->controls_rwsem);
result = snd_ctl_elem_read(card, control);
up_read(&card->controls_rwsem);
}
snd_power_unlock(card);
if (result >= 0)
if (copy_to_user(_control, control, sizeof(*control)))
Expand All @@ -931,29 +928,28 @@ static int snd_ctl_elem_write(struct snd_card *card, struct snd_ctl_file *file,
unsigned int index_offset;
int result;

down_read(&card->controls_rwsem);
kctl = snd_ctl_find_id(card, &control->id);
if (kctl == NULL) {
result = -ENOENT;
} else {
index_offset = snd_ctl_get_ioff(kctl, &control->id);
vd = &kctl->vd[index_offset];
if (!(vd->access & SNDRV_CTL_ELEM_ACCESS_WRITE) ||
kctl->put == NULL ||
(file && vd->owner && vd->owner != file)) {
result = -EPERM;
} else {
snd_ctl_build_ioff(&control->id, kctl, index_offset);
result = kctl->put(kctl, control);
}
if (result > 0) {
struct snd_ctl_elem_id id = control->id;
snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_VALUE, &id);
result = 0;
}
if (kctl == NULL)
return -ENOENT;

index_offset = snd_ctl_get_ioff(kctl, &control->id);
vd = &kctl->vd[index_offset];
if (!(vd->access & SNDRV_CTL_ELEM_ACCESS_WRITE) || kctl->put == NULL ||
(file && vd->owner && vd->owner != file)) {
return -EPERM;
}
up_read(&card->controls_rwsem);
return result;

snd_ctl_build_ioff(&control->id, kctl, index_offset);
result = kctl->put(kctl, control);
if (result < 0)
return result;

if (result > 0) {
struct snd_ctl_elem_id id = control->id;
snd_ctl_notify(card, SNDRV_CTL_EVENT_MASK_VALUE, &id);
}

return 0;
}

static int snd_ctl_elem_write_user(struct snd_ctl_file *file,
Expand All @@ -970,8 +966,11 @@ static int snd_ctl_elem_write_user(struct snd_ctl_file *file,
card = file->card;
snd_power_lock(card);
result = snd_power_wait(card, SNDRV_CTL_POWER_D0);
if (result >= 0)
if (result >= 0) {
down_read(&card->controls_rwsem);
result = snd_ctl_elem_write(card, file, control);
up_read(&card->controls_rwsem);
}
snd_power_unlock(card);
if (result >= 0)
if (copy_to_user(_control, control, sizeof(*control)))
Expand Down

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