ALSA: control: code refactoring for ELEM_READ/ELEM_WRITE operations
ALSA control core handles ELEM_READ/ELEM_WRITE requests within lock acquisition of a counting semaphore. The lock is acquired in helper functions in the end of call path before calling implementations of each driver. ioctl(2) with SNDRV_CTL_ELEM_READ ... ->snd_ctl_ioctl() ->snd_ctl_elem_read_user() ->snd_ctl_elem_read() ->down_read(controls_rwsem) ->snd_ctl_find_id() ->struct snd_kcontrol.get() ->up_read(controls_rwsem) ioctl(2) with SNDRV_CTL_ELEM_WRITE ... ->snd_ctl_ioctl() ->snd_ctl_elem_write_user() ->snd_ctl_elem_write() ->down_read(controls_rwsem) ->snd_ctl_find_id() ->struct snd_kcontrol.put() ->up_read(controls_rwsem) This commit moves the lock acquisition to middle of the call graph to simplify the helper functions. As a result: ioctl(2) with SNDRV_CTL_ELEM_READ ... ->snd_ctl_ioctl() ->snd_ctl_elem_read_user() ->down_read(controls_rwsem) ->snd_ctl_elem_read() ->snd_ctl_find_id() ->struct snd_kcontrol.get() ->up_read(controls_rwsem) ioctl(2) with SNDRV_CTL_ELEM_WRITE ... ->snd_ctl_ioctl() ->snd_ctl_elem_write_user() ->down_read(controls_rwsem) ->snd_ctl_elem_write() ->snd_ctl_find_id() ->struct snd_kcontrol.put() ->up_read(controls_rwsem) Signed-off-by: Takashi Sakamoto <o-takashi@sakamocchi.jp> Signed-off-by: Takashi Iwai <tiwai@suse.de>
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