locking/lockdep: Add nest_lock integrity test

Boqun reported that hlock->references can overflow. Add a debug test
for that to generate a clear error when this happens.

Without this, lockdep is likely to report a mysterious failure on
unlock.

Reported-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nicolai Hähnle <Nicolai.Haehnle@amd.com>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 9 insertions, 2 deletions

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 9812e5dd409e..c0ee8607c11e 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -3260,10 +3260,17 @@ static int __lock_acquire(struct lockdep_map *lock, unsigned int subclass,
         if (depth) {
                 hlock = curr->held_locks + depth - 1;
                 if (hlock->class_idx == class_idx && nest_lock) {
-                        if (hlock->references)
+                        if (hlock->references) {
+                                /*
+                                 * Check: unsigned int references:12, overflow.
+                                 */
+                                if (DEBUG_LOCKS_WARN_ON(hlock->references == (1 << 12)-1))
+                                        return 0;
+
                                 hlock->references++;
-                        else
+                        } else {
                                 hlock->references = 2;
+                        }
 
                         return 1;
                 }