linux-kernel - [PATCH 3.16 014/192] tools/lib/lockdep: Reduce MAX_LOCK_DEPTH to avoid overflowing lock

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Message-ID: <lsq.1507553064.245274727@decadent.org.uk>
Date:   Mon, 09 Oct 2017 13:44:24 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Peter Zijlstra" <peterz@...radead.org>,
        a.p.zijlstra@...llo.nl, "Sasha Levin" <sasha.levin@...cle.com>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...nel.org>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>
Subject: [PATCH 3.16 014/192] tools/lib/lockdep: Reduce MAX_LOCK_DEPTH to
 avoid overflowing lock_chain/: Depth

3.16.49-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Ben Hutchings <ben@...adent.org.uk>

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.

Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
Signed-off-by: Sasha Levin <sasha.levin@...cle.com>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: a.p.zijlstra@...llo.nl
Link: http://lkml.kernel.org/r/20170525130005.5947-3-alexander.levin@verizon.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 tools/lib/lockdep/uinclude/linux/lockdep.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/tools/lib/lockdep/uinclude/linux/lockdep.h
+++ b/tools/lib/lockdep/uinclude/linux/lockdep.h
@@ -8,7 +8,7 @@
 #include <linux/utsname.h>
 
 
-#define MAX_LOCK_DEPTH 2000UL
+#define MAX_LOCK_DEPTH 255UL
 
 #define asmlinkage
 #define __visible