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    Subject[PATCH 4.4 23/57] tools/lib/lockdep: Reduce MAX_LOCK_DEPTH to avoid overflowing lock_chain/: Depth
    Date
    4.4-stable review patch.  If anyone has any objections, please let me know.

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

    From: Ben Hutchings <ben@decadent.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@decadent.org.uk>
    Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: a.p.zijlstra@chello.nl
    Link: http://lkml.kernel.org/r/20170525130005.5947-3-alexander.levin@verizon.com
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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>
    #include <linux/compiler.h>

    -#define MAX_LOCK_DEPTH 2000UL
    +#define MAX_LOCK_DEPTH 255UL

    #define asmlinkage
    #define __visible

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