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ALSA: pcm: Revert capture stream behavior change in blocking mode

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In the commit 62ba568f7a ("ALSA: pcm: Return 0 when size <
start_threshold in capture"), we changed the behavior of
__snd_pcm_lib_xfer() to return immediately with 0 when a capture
stream has a high start_threshold.  This was intended to be a
correction of the behavior consistency and looked harmless, but this
was the culprit of the recent breakage reported by syzkaller, which
was fixed by the commit e190161f96 ("ALSA: pcm: Fix tight loop of
OSS capture stream").

At the time for the OSS fix, I didn't touch the behavior for ALSA
native API, as assuming that this behavior actually is good.  But this
turned out to be also broken actually for a similar deployment,
e.g. one thread goes to a write loop in blocking mode while another
thread controls the start/stop of the stream manually.

Overall, the original commit is harmful, and it brings less merit to
keep that behavior.  Let's revert it.

Fixes: 62ba568f7a ("ALSA: pcm: Return 0 when size < start_threshold in capture")
Fixes: e190161f96 ("ALSA: pcm: Fix tight loop of OSS capture stream")
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
This commit is contained in:
Takashi Iwai 2019-02-06 07:30:44 +01:00
parent 0a5cf9e88b
commit 00a399cad1
1 changed files with 4 additions and 16 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

16
sound/core/pcm_lib.c
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@ -2112,13 +2112,6 @@ int pcm_lib_apply_appl_ptr(struct snd_pcm_substream *substream,
return 0;
}
/* allow waiting for a capture stream that hasn't been started */
#if IS_ENABLED(CONFIG_SND_PCM_OSS)
#define wait_capture_start(substream) ((substream)->oss.oss)
#else
#define wait_capture_start(substream) false
#endif
/* the common loop for read/write data */
snd_pcm_sframes_t __snd_pcm_lib_xfer(struct snd_pcm_substream *substream,
void *data, bool interleaved,
@ -2184,16 +2177,11 @@ snd_pcm_sframes_t __snd_pcm_lib_xfer(struct snd_pcm_substream *substream,
snd_pcm_update_hw_ptr(substream);
if (!is_playback &&
runtime->status->state == SNDRV_PCM_STATE_PREPARED) {
if (size >= runtime->start_threshold) {
runtime->status->state == SNDRV_PCM_STATE_PREPARED &&
size >= runtime->start_threshold) {
err = snd_pcm_start(substream);
if (err < 0)
goto _end_unlock;
} else if (!wait_capture_start(substream)) {
/* nothing to do */
err = 0;
goto _end_unlock;
}
}
avail = snd_pcm_avail(substream);