Patch "ALSA: seq: Avoid invalid lockdep class warning" has been added to the 4.4-stable tree

Patch "ALSA: seq: Avoid invalid lockdep class warning" has been added to the 4.4-stable tree

[gregkh]

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

    ALSA: seq: Avoid invalid lockdep class warning

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-seq-avoid-invalid-lockdep-class-warning.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 <stable@vger.kernel.org> know about it.


>From 3510c7aa069aa83a2de6dab2b41401a198317bdc Mon Sep 17 00:00:00 2001
From: Takashi Iwai <tiwai@suse.de>
Date: Mon, 6 Nov 2017 20:16:50 +0100
Subject: ALSA: seq: Avoid invalid lockdep class warning

From: Takashi Iwai <tiwai@suse.de>

commit 3510c7aa069aa83a2de6dab2b41401a198317bdc upstream.

The recent fix for adding rwsem nesting annotation was using the given
"hop" argument as the lock subclass key.  Although the idea itself
works, it may trigger a kernel warning like:
  BUG: looking up invalid subclass: 8
  ....
since the lockdep has a smaller number of subclasses (8) than we
currently allow for the hops there (10).

The current definition is merely a sanity check for avoiding the too
deep delivery paths, and the 8 hops are already enough.  So, as a
quick fix, just follow the max hops as same as the max lockdep
subclasses.

Fixes: 1f20f9ff57ca ("ALSA: seq: Fix nested rwsem annotation for lockdep splat")
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 include/sound/seq_kernel.h |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/include/sound/seq_kernel.h
+++ b/include/sound/seq_kernel.h
@@ -49,7 +49,8 @@ typedef union snd_seq_timestamp snd_seq_
 #define SNDRV_SEQ_DEFAULT_CLIENT_EVENTS	200
 
 /* max delivery path length */
-#define SNDRV_SEQ_MAX_HOPS		10
+/* NOTE: this shouldn't be greater than MAX_LOCKDEP_SUBCLASSES */
+#define SNDRV_SEQ_MAX_HOPS		8
 
 /* max size of event size */
 #define SNDRV_SEQ_MAX_EVENT_LEN		0x3fffffff


Patches currently in stable-queue which might be from tiwai@suse.de are

queue-4.4/alsa-seq-avoid-invalid-lockdep-class-warning.patch
queue-4.4/alsa-seq-fix-oss-sysex-delivery-in-oss-emulation.patch