[PATCH 5.10 193/491] ALSA: pcm: fix wait_time calculations

Greg Kroah-Hartman
2026-04-13T16:50:55Z

From: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>

[ Upstream commit 3ed2b549b39f57239aad50a255ece353997183fd ]

... in wait_for_avail() and snd_pcm_drain().

t was calculated in seconds, so it would be pretty much always zero, to
be subsequently de-facto ignored due to being max(t, 10)'d. And then it
(i.e., 10) would be treated as secs, which doesn't seem right.

However, fixing it to properly calculate msecs would potentially cause
timeouts when using twice the period size for the default timeout (which
seems reasonable to me), so instead use the buffer size plus 10 percent
to be on the safe side ... but that still seems insufficient, presumably
because the hardware typically needs a moment to fire up. To compensate
for this, we up the minimal timeout to 100ms, which is still two orders
of magnitude less than the bogus minimum.

substream->wait_time was also misinterpreted as jiffies, despite being
documented as being in msecs. Only the soc/sof driver sets it - to 500,
which looks very much like msecs were intended.

Speaking of which, shouldn't snd_pcm_drain() also use substream->
wait_time?

As a drive-by, make the debug messages on timeout less confusing.

Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Link: https://lore.kernel.org/r/20230405201219.2197774-1-oswald.buddenhagen@gmx.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Stable-dep-of: 9b1dbd69ba6f ("ALSA: pcm: fix use-after-free on linked stream runtime in snd_pcm_drain()")
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
sound/core/pcm_lib.c | 11 +++++------
sound/core/pcm_native.c | 8 ++++----
2 files changed, 9 insertions(+), 10 deletions(-)

--- a/sound/core/pcm_lib.c
+++ b/sound/core/pcm_lib.c
@@ -1843,15 +1843,14 @@ static int wait_for_avail(struct snd_pcm
if (substream->wait_time) {
wait_time = substream->wait_time;
} else {
- wait_time = 10;
+ wait_time = 100;

if (runtime->rate) {
- long t = runtime->period_size * 2 /
- runtime->rate;
+ long t = runtime->buffer_size * 1100 / runtime->rate;
wait_time = max(t, wait_time);
}
- wait_time = msecs_to_jiffies(wait_time * 1000);
}
+ wait_time = msecs_to_jiffies(wait_time);
}

for (;;) {
@@ -1899,8 +1898,8 @@ static int wait_for_avail(struct snd_pcm
}
if (!tout) {
pcm_dbg(substream->pcm,
- "%s write error (DMA or IRQ trouble?)\n",
- is_playback ? "playback" : "capture");
+ "%s timeout (DMA or IRQ trouble?)\n",
+ is_playback ? "playback write" : "capture read");
err = -EIO;
break;
}
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -2155,12 +2155,12 @@ static int snd_pcm_drain(struct snd_pcm_
if (runtime->no_period_wakeup)
tout = MAX_SCHEDULE_TIMEOUT;
else {
- tout = 10;
+ tout = 100;
if (runtime->rate) {
- long t = runtime->period_size * 2 / runtime->rate;
+ long t = runtime->buffer_size * 1100 / runtime->rate;
tout = max(t, tout);
}
- tout = msecs_to_jiffies(tout * 1000);
+ tout = msecs_to_jiffies(tout);
}
tout = schedule_timeout(tout);

@@ -2183,7 +2183,7 @@ static int snd_pcm_drain(struct snd_pcm_
result = -ESTRPIPE;
else {
dev_dbg(substream->pcm->card->dev,
- "playback drain error (DMA or IRQ trouble?)\n");
+ "playback drain timeout (DMA or IRQ trouble?)\n");
snd_pcm_stop(substream, SNDRV_PCM_STATE_SETUP);
result = -EIO;
}