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Subject[PATCH 2/8] liblockdep: Reduce MAX_LOCK_DEPTH to avoid overflowing lock_chain::depth
From: Ben Hutchings <>

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.

Cc: <> # for versions before 4.6, use a value of 255
Signed-off-by: Ben Hutchings <>
Signed-off-by: Sasha Levin <>
tools/lib/lockdep/uinclude/linux/lockdep.h | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/lib/lockdep/uinclude/linux/lockdep.h b/tools/lib/lockdep/uinclude/linux/lockdep.h
index c808c7d..d302142 100644
--- a/tools/lib/lockdep/uinclude/linux/lockdep.h
+++ b/tools/lib/lockdep/uinclude/linux/lockdep.h
@@ -8,7 +8,7 @@
#include <linux/utsname.h>
#include <linux/compiler.h>

-#define MAX_LOCK_DEPTH 2000UL
+#define MAX_LOCK_DEPTH 63UL

#define asmlinkage
#define __visible
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