FAILED: patch "[PATCH] ALSA: hda/hdmi: fix incorrect locking in hdmi_pcm_close" failed to apply to 4.9-stable tree

The patch below does not apply to the 4.9-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From ce1558c285f9ad04c03b46833a028230771cc0a7 Mon Sep 17 00:00:00 2001
From: Kai Vehmanen <[email protected]>
Date: Tue, 13 Oct 2020 18:26:28 +0300
Subject: [PATCH] ALSA: hda/hdmi: fix incorrect locking in hdmi_pcm_close

A race exists between closing a PCM and update of ELD data. In hdmi_pcm_close(), hinfo->nid value is modified without taking spec->pcm_lock. If this happens concurrently while processing an ELD update in hdmi_pcm_setup_pin(), converter assignment may be done incorrectly.

This bug was found by hitting a WARN_ON in snd_hda_spdif_ctls_assign() in a HDMI receiver connection stress test:

[2739.684569] WARNING: CPU: 5 PID: 2090 at sound/pci/hda/patch_hdmi.c:1898 check_non_pcm_per_cvt+0x41/0x50 [snd_hda_codec_hdmi]
...
[2739.684707] Call Trace:
[2739.684720]  update_eld+0x121/0x5a0 [snd_hda_codec_hdmi]
[2739.684736]  hdmi_present_sense+0x21e/0x3b0 [snd_hda_codec_hdmi]
[2739.684750]  check_presence_and_report+0x81/0xd0 [snd_hda_codec_hdmi]
[2739.684842]  intel_audio_codec_enable+0x122/0x190 [i915]

index 0ffbfcb91256..ccd1df059654 100644
@@ -2046,22 +2046,25 @@ static int hdmi_pcm_close(struct hda_pcm_stream *hinfo,
 	int pinctl;
 	int err = 0;
 
+	mutex_lock(&spec->pcm_lock);
 	if (hinfo->nid) {
 		pcm_idx = hinfo_to_pcm_index(codec, hinfo);
-		if (snd_BUG_ON(pcm_idx < 0))
-			return -EINVAL;
+		if (snd_BUG_ON(pcm_idx < 0)) {
+			err = -EINVAL;
+			goto unlock;
+		}
 		cvt_idx = cvt_nid_to_cvt_index(codec, hinfo->nid);
-		if (snd_BUG_ON(cvt_idx < 0))
-			return -EINVAL;
+		if (snd_BUG_ON(cvt_idx < 0)) {
+			err = -EINVAL;
+			goto unlock;
+		}
 		per_cvt = get_cvt(spec, cvt_idx);
-
 		snd_BUG_ON(!per_cvt->assigned);
 		per_cvt->assigned = 0;
 		hinfo->nid = 0;
 
 		azx_stream(get_azx_dev(substream))->stripe = 0;
 
-		mutex_lock(&spec->pcm_lock);
 		snd_hda_spdif_ctls_unassign(codec, pcm_idx);
 		clear_bit(pcm_idx, &spec->pcm_in_use);
 		pin_idx = hinfo_to_pin_index(codec, hinfo);

@@ -2091,10 +2094,11 @@ static int hdmi_pcm_close(struct hda_pcm_stream *hinfo,
 		per_pin->setup = false;
 		per_pin->channels = 0;
 		mutex_unlock(&per_pin->lock);
-	unlock:
-		mutex_unlock(&spec->pcm_lock);
 	}
 
+unlock:
+	mutex_unlock(&spec->pcm_lock);
+
 	return err;
 }