Merge tag 'armsoc-fixes' of git://git.kernel.org/pub/scm/linux/kernel/git/arm/arm-soc

[linux-2.6-block.git] / sound / core / pcm_native.c

diff --git a/sound/core/pcm_native.c b/sound/core/pcm_native.c
index fadd3eb8e8bb2d77264fafec9be05ba54e36af85..9106d8e2300eab3e566f9a3807c469ee02aa7bcd 100644 (file)
--- a/sound/core/pcm_native.c
+++ b/sound/core/pcm_native.c
@@ -74,6 +74,18 @@ static int snd_pcm_open(struct file *file, struct snd_pcm *pcm, int stream);
 static DEFINE_RWLOCK(snd_pcm_link_rwlock);
 static DECLARE_RWSEM(snd_pcm_link_rwsem);
 
+/* Writer in rwsem may block readers even during its waiting in queue,
+ * and this may lead to a deadlock when the code path takes read sem
+ * twice (e.g. one in snd_pcm_action_nonatomic() and another in
+ * snd_pcm_stream_lock()).  As a (suboptimal) workaround, let writer to
+ * spin until it gets the lock.
+ */
+static inline void down_write_nonblock(struct rw_semaphore *lock)
+{
+       while (!down_write_trylock(lock))
+               cond_resched();
+}
+
 /**
  * snd_pcm_stream_lock - Lock the PCM stream
  * @substream: PCM substream
@@ -1813,7 +1825,7 @@ static int snd_pcm_link(struct snd_pcm_substream *substream, int fd)
                res = -ENOMEM;
                goto _nolock;
        }
-       down_write(&snd_pcm_link_rwsem);
+       down_write_nonblock(&snd_pcm_link_rwsem);
        write_lock_irq(&snd_pcm_link_rwlock);
        if (substream->runtime->status->state == SNDRV_PCM_STATE_OPEN ||
            substream->runtime->status->state != substream1->runtime->status->state ||
@@ -1860,7 +1872,7 @@ static int snd_pcm_unlink(struct snd_pcm_substream *substream)
        struct snd_pcm_substream *s;
        int res = 0;
 
-       down_write(&snd_pcm_link_rwsem);
+       down_write_nonblock(&snd_pcm_link_rwsem);
        write_lock_irq(&snd_pcm_link_rwlock);
        if (!snd_pcm_stream_linked(substream)) {
                res = -EALREADY;