ASoC: soc-pcm: Move debugfs removal out of spinlock

The recent fix for DPCM locking also covered the loop in
dpcm_be_disconnect() with the FE stream lock.  This caused an
unexpected side effect, thought: calling debugfs_remove_recursive() in
the spinlock may lead to lockdep splats as the code there assumes the
SOFTIRQ-safe context.

For avoiding the problem, this patch changes the disconnection
procedure to two phases: at first, the matching entries are removed
from the linked list, then the resources are freed outside the lock.

Fixes: b7898396 ("ASoC: soc-pcm: Fix and cleanup DPCM locking")
Reported-and-tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Link: https://lore.kernel.org/r/20220119155249.26754-3-tiwai@suse.deSigned-off-by: Mark Brown <broonie@kernel.org>

sound/soc/soc-pcm.c

@@ -1268,6 +1268,7 @@ static void dpcm_be_reparent(struct snd_soc_pcm_runtime *fe,
 void dpcm_be_disconnect(struct snd_soc_pcm_runtime *fe, int stream)
 {
 	struct snd_soc_dpcm *dpcm, *d;
+	LIST_HEAD(deleted_dpcms);
 
 	snd_soc_dpcm_mutex_assert_held(fe);
 
@@ -1287,13 +1288,18 @@ void dpcm_be_disconnect(struct snd_soc_pcm_runtime *fe, int stream)
 		/* BEs still alive need new FE */
 		dpcm_be_reparent(fe, dpcm->be, stream);
 
-		dpcm_remove_debugfs_state(dpcm);
-
 		list_del(&dpcm->list_be);
+		list_move(&dpcm->list_fe, &deleted_dpcms);
+	}
+	snd_soc_dpcm_stream_unlock_irq(fe, stream);
+
+	while (!list_empty(&deleted_dpcms)) {
+		dpcm = list_first_entry(&deleted_dpcms, struct snd_soc_dpcm,
+					list_fe);
 		list_del(&dpcm->list_fe);
+		dpcm_remove_debugfs_state(dpcm);
 		kfree(dpcm);
 	}
-	snd_soc_dpcm_stream_unlock_irq(fe, stream);
 }
 
 /* get BE for DAI widget and stream */