lockdep: spin_lock_nest_lock()

Expose the new lock protection lock.

This can be used to annotate places where we take multiple locks of the
same class and avoid deadlocks by always taking another (top-level) lock
first.

NOTE: we're still bound to the MAX_LOCK_DEPTH (48) limit.

Signed-off-by: Peter Zijlstra <[e-mail]>
Signed-off-by: Ingo Molnar <[e-mail]>

include/linux/lockdep.h

···
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 # ifdef CONFIG_PROVE_LOCKING
 #  define spin_acquire(l, s, t, i)		lock_acquire(l, s, t, 0, 2, NULL, i)
+#  define spin_acquire_nest(l, s, t, n, i)	lock_acquire(l, s, t, 0, 2, n, i)
 # else
 #  define spin_acquire(l, s, t, i)		lock_acquire(l, s, t, 0, 1, NULL, i)
+#  define spin_acquire_nest(l, s, t, n, i)	lock_acquire(l, s, t, 0, 1, NULL, i)
 # endif
 # define spin_release(l, n, i)			lock_release(l, n, i)
 #else

include/linux/spinlock.h

···
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 # define spin_lock_nested(lock, subclass) _spin_lock_nested(lock, subclass)
+# define spin_lock_nest_lock(lock, nest_lock)				\
+	 do {								\
+		 typecheck(struct lockdep_map *, &(nest_lock)->dep_map);\
+		 _spin_lock_nest_lock(lock, &(nest_lock)->dep_map);	\
+	 } while (0)
 #else
 # define spin_lock_nested(lock, subclass) _spin_lock(lock)
+# define spin_lock_nest_lock(lock, nest_lock) _spin_lock(lock)
 #endif
 
 #define write_lock(lock)		_write_lock(lock)

include/linux/spinlock_api_smp.h

···
 void __lockfunc _spin_lock(spinlock_t *lock)		__acquires(lock);
 void __lockfunc _spin_lock_nested(spinlock_t *lock, int subclass)
 							__acquires(lock);
+void __lockfunc _spin_lock_nest_lock(spinlock_t *lock, struct lockdep_map *map)
+							__acquires(lock);
 void __lockfunc _read_lock(rwlock_t *lock)		__acquires(lock);
 void __lockfunc _write_lock(rwlock_t *lock)		__acquires(lock);
 void __lockfunc _spin_lock_bh(spinlock_t *lock)		__acquires(lock);

kernel/spinlock.c

···
 }
 
 EXPORT_SYMBOL(_spin_lock_nested);
+
 unsigned long __lockfunc _spin_lock_irqsave_nested(spinlock_t *lock, int subclass)
 {
 	unsigned long flags;
···
 }
 
 EXPORT_SYMBOL(_spin_lock_irqsave_nested);
+
+void __lockfunc _spin_lock_nest_lock(spinlock_t *lock,
+				     struct lockdep_map *nest_lock)
+{
+	preempt_disable();
+	spin_acquire_nest(&lock->dep_map, 0, 0, nest_lock, _RET_IP_);
+	LOCK_CONTENDED(lock, _raw_spin_trylock, _raw_spin_lock);
+}
+
+EXPORT_SYMBOL(_spin_lock_nest_lock);
 
 #endif