Re: [PATCH] ALSA: pcm: Fix starvation on down_write_nonblock()

[kbuild test robot]

Hi Chanho,

I love your patch! Yet something to improve:

[auto build test ERROR on sound/for-next]
[also build test ERROR on v4.20-rc3 next-20181123]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Chanho-Min/ALSA-pcm-Fix-starvation-on-down_write_nonblock/20181124-182630
base:   https://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound.git for-next
config: x86_64-randconfig-x001-201846 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-1) 7.3.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All errors (new ones prefixed by >>):

   sound/core/pcm_native.c: In function 'down_write_nonblock':
>> sound/core/pcm_native.c:99:3: error: implicit declaration of function 'msleep' [-Werror=implicit-function-declaration]
      msleep(1);
      ^~~~~~
   cc1: some warnings being treated as errors

vim +/msleep +99 sound/core/pcm_native.c

    89	
    90	/* Writer in rwsem may block readers even during its waiting in queue,
    91	 * and this may lead to a deadlock when the code path takes read sem
    92	 * twice (e.g. one in snd_pcm_action_nonatomic() and another in
    93	 * snd_pcm_stream_lock()).  As a (suboptimal) workaround, let writer to
    94	 * spin until it gets the lock.
    95	 */
    96	static inline void down_write_nonblock(struct rw_semaphore *lock)
    97	{
    98		while (!down_write_trylock(lock))
  > 99			msleep(1);
   100	}
   101	

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