The variable codec->regmap is often protected by the lock
codec->regmap_lock when is accessed. However, it is accessed without
holding the lock when is accessed in snd_hdac_regmap_sync():

  if (codec->regmap)

In my opinion, this may be a harmful race, because if codec->regmap is
set to NULL right after the condition is checked, a null-pointer
dereference can occur in the called function regcache_sync():

  map->lock(map->lock_arg); --> Line 360 in drivers/base/regmap/regcache.c

To fix this possible null-pointer dereference caused by data race, the
mutex_lock coverage is extended to protect the if statement as well as the
function call to regcache_sync().

[ Note: the lack of the regmap_lock itself is harmless for the current
  codec driver implementations, as snd_hdac_regmap_sync() is only for
  PM runtime resume that is prohibited during the codec probe.
  But the change makes the whole code more consistent, so it's merged
  as is -- tiwai ]
Reported-by: BassCheck <bass@buaa.edu.cn>
Signed-off-by: Tuo Li <islituo@gmail.com>
Link: https://lore.kernel.org/r/20230703031016.1184711-1-islituo@gmail.comSigned-off-by: Takashi Iwai <tiwai@suse.de>