This is a note to let you know that I've just added the patch titled
ALSA: hda: Fix hang at HD-audio codec unbinding due to refcount saturation
to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
alsa-hda-fix-hang-at-hd-audio-codec-unbinding-due-to.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 2d6dc8e2c1d63544239af803b55c09ec1a9d4277
Author: Takashi Iwai <tiwai@xxxxxxx>
Date: Sat Sep 10 16:25:50 2022 +0200
ALSA: hda: Fix hang at HD-audio codec unbinding due to refcount saturation
[ Upstream commit ead3d3c5b54f76da79c079e61bacb4279ec56965 ]
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@xxxxxxxxxxxxxxx>
Tested-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/YxtflWQnslMHVlU7@xxxxxxxxx
Link: https://lore.kernel.org/r/20220910142550.28494-1-tiwai@xxxxxxx
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/sound/pci/hda/hda_bind.c b/sound/pci/hda/hda_bind.c
index c572fb5886d5..7af251573595 100644
--- 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)
