Patch "tools/lib/lockdep: Reduce MAX_LOCK_DEPTH to avoid overflowing lock_chain/: Depth" 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

tools/lib/lockdep: Reduce MAX_LOCK_DEPTH to avoid overflowing lock_chain/: Depth

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:
tools-lib-lockdep-reduce-max_lock_depth-to-avoid-overflowing-lock_chain-depth.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: Ben Hutchings <[email protected]>
Date: Thu, 25 May 2017 12:58:33 +0000
Subject: tools/lib/lockdep: Reduce MAX_LOCK_DEPTH to avoid overflowing lock_chain/: Depth

From: Ben Hutchings <[email protected]>

commit 98dcea0cfd04e083ac74137ceb9a632604740e2d upstream.

liblockdep has been broken since commit 75dd602a5198 ("lockdep: Fix lock_chain::base size"), as that adds a check that MAX_LOCK_DEPTH is within the range of lock_chain::depth and in liblockdep it is much too large.

That should have resulted in a compiler error, but didn't because:

- the check uses ARRAY_SIZE(), which isn't yet defined in liblockdep so is assumed to be an (undeclared) function
- putting a function call inside a BUILD_BUG_ON() expression quietly turns it into some nonsense involving a variable-length array

It did produce a compiler warning, but I didn't notice because liblockdep already produces too many warnings if -Wall is enabled (which I'll fix shortly).

Even before that commit, which reduced lock_chain::depth from 8 bits to 6, MAX_LOCK_DEPTH was too large.

---
 tools/lib/lockdep/uinclude/linux/lockdep.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

@@ -8,7 +8,7 @@
 #include <linux/utsname.h>
 #include <linux/compiler.h>
 
-#define MAX_LOCK_DEPTH 2000UL
+#define MAX_LOCK_DEPTH 255UL
 
 #define asmlinkage
 #define __visible

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

queue-4.4/tools-lib-lockdep-reduce-max_lock_depth-to-avoid-overflowing-lock_chain-depth.patch