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In the commit62ba568f7a("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 commite190161f96("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>