Patch "ALSA: pcm: Remove incorrect snd_BUG_ON() usages" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

ALSA: pcm: Remove incorrect snd_BUG_ON() usages

to the 4.4-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-pcm-remove-incorrect-snd_bug_on-usages.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Takashi Iwai <[email protected]>
Date: Mon, 1 Jan 2018 09:50:50 +0100
Subject: ALSA: pcm: Remove incorrect snd_BUG_ON() usages

From: Takashi Iwai <[email protected]>

commit fe08f34d066f4404934a509b6806db1a4f700c86 upstream.

syzkaller triggered kernel warnings through PCM OSS emulation at closing a stream:

  WARNING: CPU: 0 PID: 3502 at sound/core/pcm_lib.c:1635
  snd_pcm_hw_param_first+0x289/0x690 sound/core/pcm_lib.c:1635
  Call Trace:
  ....
   snd_pcm_hw_param_near.constprop.27+0x78d/0x9a0 sound/core/oss/pcm_oss.c:457
   snd_pcm_oss_change_params+0x17d3/0x3720 sound/core/oss/pcm_oss.c:969
   snd_pcm_oss_make_ready+0xaa/0x130 sound/core/oss/pcm_oss.c:1128
   snd_pcm_oss_sync+0x257/0x830 sound/core/oss/pcm_oss.c:1638
   snd_pcm_oss_release+0x20b/0x280 sound/core/oss/pcm_oss.c:2431
   __fput+0x327/0x7e0 fs/file_table.c:210
   ....

This happens while it tries to open and set up the aloop device concurrently. The warning above (invoked from snd_BUG_ON() macro) is to detect the unexpected logical error where snd_pcm_hw_refine() call shouldn't fail. The theory is true for the case where the hw_params config rules are static. But for an aloop device, the hw_params rule condition does vary dynamically depending on the connected target; when another device is opened and changes the parameters, the device connected in another side is also affected, and it caused the error from snd_pcm_hw_refine().

That is, the simplest "solution" for this is to remove the incorrect assumption of static rules, and treat such an error as a normal error path. As there are a couple of other places using snd_BUG_ON() incorrectly, this patch removes these spurious snd_BUG_ON() calls.

---
 sound/core/oss/pcm_oss.c |    1 -
 sound/core/pcm_lib.c     |    4 ++--
 2 files changed, 2 insertions(+), 3 deletions(-)

@@ -465,7 +465,6 @@ static int snd_pcm_hw_param_near(struct
 		v = snd_pcm_hw_param_last(pcm, params, var, dir);
 	else
 		v = snd_pcm_hw_param_first(pcm, params, var, dir);
-	snd_BUG_ON(v < 0);
 	return v;
 }
 

@@ -1664,7 +1664,7 @@ int snd_pcm_hw_param_first(struct snd_pc
 		return changed;
 	if (params->rmask) {
 		int err = snd_pcm_hw_refine(pcm, params);
-		if (snd_BUG_ON(err < 0))
+		if (err < 0)
 			return err;
 	}
 	return snd_pcm_hw_param_value(params, var, dir);

@@ -1711,7 +1711,7 @@ int snd_pcm_hw_param_last(struct snd_pcm
 		return changed;
 	if (params->rmask) {
 		int err = snd_pcm_hw_refine(pcm, params);
-		if (snd_BUG_ON(err < 0))
+		if (err < 0)
 			return err;
 	}
 	return snd_pcm_hw_param_value(params, var, dir);

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/alsa-pcm-remove-incorrect-snd_bug_on-usages.patch queue-4.4/alsa-aloop-fix-inconsistent-format-due-to-incomplete-rule.patch queue-4.4/alsa-pcm-add-missing-error-checks-in-oss-emulation-plugin-builder.patch queue-4.4/alsa-pcm-abort-properly-at-pending-signal-in-oss-read-write-loops.patch queue-4.4/alsa-pcm-allow-aborting-mutex-lock-at-oss-read-write-loops.patch queue-4.4/alsa-aloop-fix-racy-hw-constraints-adjustment.patch queue-4.4/alsa-aloop-release-cable-upon-open-error-path.patch