ALSA: PCM: check if ops are defined before suspending PCM

BugLink: https://bugs.launchpad.net/bugs/1828420

[ Upstream commit d9c0b2af ]

BE dai links only have internal PCM's and their substream ops may
not be set. Suspending these PCM's will result in their
 ops->trigger() being invoked and cause a kernel oops.
So skip suspending PCM's if their ops are NULL.

[ NOTE: this change is required now for following the recent PCM core
  change to get rid of snd_pcm_suspend() call.  Since DPCM BE takes
  the runtime carried from FE while keeping NULL ops, it can hit this
  bug.  See details at:
     https://github.com/thesofproject/linux/pull/582
  -- tiwai ]
Signed-off-by: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

sound/core/pcm_native.c

@@ -1342,6 +1342,14 @@ int snd_pcm_suspend_all(struct snd_pcm *pcm)
 			/* FIXME: the open/close code should lock this as well */
 			if (substream->runtime == NULL)
 				continue;
+
+			/*
+			 * Skip BE dai link PCM's that are internal and may
+			 * not have their substream ops set.
+			 */
+			if (!substream->ops)
+				continue;
+
 			err = snd_pcm_suspend(substream);
 			if (err < 0 && err != -EBUSY)
 				return err;