ALSA: hda: Fix hang at HD-audio codec unbinding due to refcount saturation

We fixed the potential deadlock at dynamic unbinding the HD-audio
codec at the commit 7206998f578d ("ALSA: hda: Fix potential deadlock
at codec unbinding"), but ironically, this caused another potential
deadlock.  The current code uses refcount_dec() and waits for the
pending task with wait_event for dropping the refcount to 0.  This
works fine when PCMs are assigned and actually waiting for the
refcount drop.

Meanwhile, when there was no PCM assigned, the refcount_dec() call
itself was supposed to drop to zero -- alas, it doesn't in reality;
refcount_dec() complains, spews kernel warning and it saturates
instead of dropping to 0, due to the nature of refcount_dec()
implementation.  This eventually blocks the wait_event() wakeup and
the code get stuck there.

For avoiding the problem, we call refcount_dec_and_test() and skips
the sync-wait if it already reaches to zero.

The patch does a slight code reshuffling to make sure to invoke other
disconnect calls before the sync-wait, too.

Fixes: 7206998f578d ("ALSA: hda: Fix potential deadlock at codec unbinding")
Reported-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Tested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/YxtflWQnslMHVlU7@intel.com
Link: https://lore.kernel.org/r/20220910142550.28494-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>

diff --git a/sound/pci/hda/hda_bind.c b/sound/pci/hda/hda_bind.c
index cae9a975cbcca809bdd59993e1343eebd4c6ad76..1a868dd9dc4b6886a8dda83514052910e52014cc 100644 (file)
--- a/sound/pci/hda/hda_bind.c
+++ b/sound/pci/hda/hda_bind.c
@@ -157,10 +157,10 @@ static int hda_codec_driver_remove(struct device *dev)
                return codec->bus->core.ext_ops->hdev_detach(&codec->core);
        }
 
-       refcount_dec(&codec->pcm_ref);
        snd_hda_codec_disconnect_pcms(codec);
        snd_hda_jack_tbl_disconnect(codec);
-       wait_event(codec->remove_sleep, !refcount_read(&codec->pcm_ref));
+       if (!refcount_dec_and_test(&codec->pcm_ref))
+               wait_event(codec->remove_sleep, !refcount_read(&codec->pcm_ref));
        snd_power_sync_ref(codec->bus->card);
 
        if (codec->patch_ops.free)