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ALSA: echoaudio: Race conditions around "opencount" 

Use of atomics does not make these statements robust:

       atomic_inc(&chip->opencount);
       if (atomic_read(&chip->opencount) > 1 && chip->rate_set)
               chip->can_set_rate=0;

and

       if (atomic_read(&chip->opencount)) {
               if (chip->opencount) {
                       changed = -EAGAIN;
               } else {
                       changed = set_digital_mode(chip, dmode);

It would be necessary to atomically increment or decrement the value
and use the returned result. And yet we still need to prevent other
threads making use of "can_set_rate" while we set it.

However in all but one case the atomic is misleading as they are already
running with "mode_mutex" held.

Decisions are made on mode setting are often intrinsically connected
to "opencount" because some operations are not permitted unless
there is sole ownership.

So instead simplify this, and use "mode_mutex" as a lock for all reference
counting and mode setting.

Signed-off-by: Mark Hills <mark@xwax.org>
Link: https://lore.kernel.org/r/20200708101848.3457-2-mark@xwax.org
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Mark Hills 2020-07-08 11:18:45 +01:00 committed by Takashi Iwai
parent db091b0e14
commit 027c70021b
2 changed files with 47 additions and 39 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

80
sound/pci/echoaudio/echoaudio.c
View File

@ -245,13 +245,20 @@ static int hw_rule_sample_rate(struct snd_pcm_hw_params *params,
SNDRV_PCM_HW_PARAM_RATE);
struct echoaudio *chip = rule->private;
struct snd_interval fixed;
int err;
if (!chip->can_set_rate) {
mutex_lock(&chip->mode_mutex);
if (chip->can_set_rate) {
err = 0;
} else {
snd_interval_any(&fixed);
fixed.min = fixed.max = chip->sample_rate;
return snd_interval_refine(rate, &fixed);
err = snd_interval_refine(rate, &fixed);
}
return 0;
mutex_unlock(&chip->mode_mutex);
return err;
}
@ -322,7 +329,7 @@ static int pcm_open(struct snd_pcm_substream *substream,
SNDRV_PCM_HW_PARAM_RATE, -1)) < 0)
return err;
/* Finally allocate a page for the scatter-gather list */
/* Allocate a page for the scatter-gather list */
if ((err = snd_dma_alloc_pages(SNDRV_DMA_TYPE_DEV,
&chip->pci->dev,
PAGE_SIZE, &pipe->sgpage)) < 0) {
@ -330,6 +337,17 @@ static int pcm_open(struct snd_pcm_substream *substream,
return err;
}
/*
* Sole ownership required to set the rate
*/
dev_dbg(chip->card->dev, "pcm_open opencount=%d can_set_rate=%d, rate_set=%d",
chip->opencount, chip->can_set_rate, chip->rate_set);
chip->opencount++;
if (chip->opencount > 1 && chip->rate_set)
chip->can_set_rate = 0;
return 0;
}
@ -353,12 +371,7 @@ static int pcm_analog_in_open(struct snd_pcm_substream *substream)
hw_rule_capture_format_by_channels, NULL,
SNDRV_PCM_HW_PARAM_CHANNELS, -1)) < 0)
return err;
atomic_inc(&chip->opencount);
if (atomic_read(&chip->opencount) > 1 && chip->rate_set)
chip->can_set_rate=0;
dev_dbg(chip->card->dev, "pcm_analog_in_open cs=%d oc=%d r=%d\n",
chip->can_set_rate, atomic_read(&chip->opencount),
chip->sample_rate);
return 0;
}
@ -388,12 +401,7 @@ static int pcm_analog_out_open(struct snd_pcm_substream *substream)
NULL,
SNDRV_PCM_HW_PARAM_CHANNELS, -1)) < 0)
return err;
atomic_inc(&chip->opencount);
if (atomic_read(&chip->opencount) > 1 && chip->rate_set)
chip->can_set_rate=0;
dev_dbg(chip->card->dev, "pcm_analog_out_open cs=%d oc=%d r=%d\n",
chip->can_set_rate, atomic_read(&chip->opencount),
chip->sample_rate);
return 0;
}
@ -429,10 +437,6 @@ static int pcm_digital_in_open(struct snd_pcm_substream *substream)
SNDRV_PCM_HW_PARAM_CHANNELS, -1)) < 0)
goto din_exit;
atomic_inc(&chip->opencount);
if (atomic_read(&chip->opencount) > 1 && chip->rate_set)
chip->can_set_rate=0;
din_exit:
mutex_unlock(&chip->mode_mutex);
return err;
@ -471,9 +475,7 @@ static int pcm_digital_out_open(struct snd_pcm_substream *substream)
NULL, SNDRV_PCM_HW_PARAM_CHANNELS,
-1)) < 0)
goto dout_exit;
atomic_inc(&chip->opencount);
if (atomic_read(&chip->opencount) > 1 && chip->rate_set)
chip->can_set_rate=0;
dout_exit:
mutex_unlock(&chip->mode_mutex);
return err;
@ -488,23 +490,29 @@ dout_exit:
static int pcm_close(struct snd_pcm_substream *substream)
{
struct echoaudio *chip = snd_pcm_substream_chip(substream);
int oc;
/* Nothing to do here. Audio is already off and pipe will be
* freed by its callback
*/
atomic_dec(&chip->opencount);
oc = atomic_read(&chip->opencount);
dev_dbg(chip->card->dev, "pcm_close oc=%d cs=%d rs=%d\n", oc,
chip->can_set_rate, chip->rate_set);
if (oc < 2)
chip->can_set_rate = 1;
if (oc == 0)
chip->rate_set = 0;
dev_dbg(chip->card->dev, "pcm_close2 oc=%d cs=%d rs=%d\n", oc,
chip->can_set_rate, chip->rate_set);
mutex_lock(&chip->mode_mutex);
dev_dbg(chip->card->dev, "pcm_open opencount=%d can_set_rate=%d, rate_set=%d",
chip->opencount, chip->can_set_rate, chip->rate_set);
chip->opencount--;
switch (chip->opencount) {
case 1:
chip->can_set_rate = 1;
break;
case 0:
chip->rate_set = 0;
break;
}
mutex_unlock(&chip->mode_mutex);
return 0;
}
@ -1409,7 +1417,7 @@ static int snd_echo_digital_mode_put(struct snd_kcontrol *kcontrol,
/* Do not allow the user to change the digital mode when a pcm
device is open because it also changes the number of channels
and the allowed sample rates */
if (atomic_read(&chip->opencount)) {
if (chip->opencount) {
changed = -EAGAIN;
} else {
changed = set_digital_mode(chip, dmode);
@ -1874,7 +1882,7 @@ static int snd_echo_create(struct snd_card *card,
chip->card = card;
chip->pci = pci;
chip->irq = -1;
atomic_set(&chip->opencount, 0);
chip->opencount = 0;
mutex_init(&chip->mode_mutex);
chip->can_set_rate = 1;
} else {

6
sound/pci/echoaudio/echoaudio.h
View File

@ -336,7 +336,7 @@ struct echoaudio {
struct mutex mode_mutex;
u16 num_digital_modes, digital_mode_list[6];
u16 num_clock_sources, clock_source_list[10];
atomic_t opencount;
unsigned int opencount; /* protected by mode_mutex */
struct snd_kcontrol *clock_src_ctl;
struct snd_pcm *analog_pcm, *digital_pcm;
struct snd_card *card;
@ -353,8 +353,8 @@ struct echoaudio {
struct timer_list timer;
char tinuse; /* Timer in use */
char midi_full; /* MIDI output buffer is full */
char can_set_rate;
char rate_set;
char can_set_rate; /* protected by mode_mutex */
char rate_set; /* protected by mode_mutex */
/* This stuff is used mainly by the lowlevel code */
struct comm_page *comm_page; /* Virtual address of the memory