ALSA: pcm: Fix lockdep warning with nonatomic PCM ops
authorTakashi Iwai <tiwai@suse.de>
Fri, 17 Jul 2015 13:22:33 +0000 (15:22 +0200)
committerTakashi Iwai <tiwai@suse.de>
Fri, 17 Jul 2015 13:36:54 +0000 (15:36 +0200)
commit67756e3191c90e7c0b94b8b2fb63de255b6cd337
tree7dbfd888abec6ba2edfeee85967f6a72d55758e4
parent98973f2f083a5ec580da8bbb685e6baa93613546
ALSA: pcm: Fix lockdep warning with nonatomic PCM ops

With the nonatomic PCM ops, the system may spew lockdep warnings like:

 =============================================
 [ INFO: possible recursive locking detected ]
 4.2.0-rc1-jeejaval3 #12 Not tainted
 ---------------------------------------------
 aplay/4029 is trying to acquire lock:
  (snd_pcm_link_rwsem){.+.+.+}, at: [<ffffffff816fd473>] snd_pcm_stream_lock+0x43/0x60

 but task is already holding lock:
  (snd_pcm_link_rwsem){.+.+.+}, at: [<ffffffff816fcf29>] snd_pcm_action_nonatomic+0x29/0x80

 other info that might help us debug this:
  Possible unsafe locking scenario:

        CPU0
        ----
   lock(snd_pcm_link_rwsem);
   lock(snd_pcm_link_rwsem);

Although this is false-positive as the rwsem is taken always as
read-only for these code paths, it's certainly annoying to see this at
any occasion.  A simple fix is to use down_read_nested() in
snd_pcm_stream_lock() that can be called inside another lock.

Reported-by: Vinod Koul <vinod.koul@intel.com>
Reported-by: Jeeja Kp <jeeja.kp@intel.com>
Tested-by: Jeeja Kp <jeeja.kp@intel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
sound/core/pcm_native.c