ALSA: pcm: oss: use proper stream lock for runtime->state access

ALSA: pcm: oss: use proper stream lock for runtime->state access

__snd_pcm_set_state() writes runtime->state under the PCM stream lock.
However, the OSS I/O functions snd_pcm_oss_write3(), snd_pcm_oss_read3(),
snd_pcm_oss_writev3() and snd_pcm_oss_readv3() read runtime->state
without holding the stream lock, only holding oss.params_lock (a
different mutex that does not synchronize with the stream lock).

Since __snd_pcm_set_state() is called from IRQ context (e.g.,
snd_pcm_period_elapsed -> snd_pcm_update_state -> __snd_pcm_xrun ->
snd_pcm_stop -> snd_pcm_post_stop) while the OSS read/write paths
run in process context, these are concurrent accesses that constitute
a data race.

Rather than using READ_ONCE()/WRITE_ONCE() barriers, introduce a
snd_pcm_get_state() helper that reads runtime->state under the stream
lock, matching the locking discipline used elsewhere in the PCM layer.
Also export snd_pcm_set_state() for completeness.

Use snd_pcm_get_state() in all four OSS I/O functions, caching the
result in a local variable where the same snapshot is used for
multiple comparisons to avoid taking the lock repeatedly.

Signed-off-by: Cen Zhang <zzzccc427@gmail.com>
Link: https://patch.msgid.link/20260316085047.2876451-1-zzzccc427@gmail.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>