lockdep: lock protection locks

On Fri, 2008-08-01 at 16:26 -0700, Linus Torvalds wrote:

> On Fri, 1 Aug 2008, David Miller wrote:
> >
> > Taking more than a few locks of the same class at once is bad
> > news and it's better to find an alternative method.
>
> It's not always wrong.
>
> If you can guarantee that anybody that takes more than one lock of a
> particular class will always take a single top-level lock _first_, then
> that's all good. You can obviously screw up and take the same lock _twice_
> (which will deadlock), but at least you cannot get into ABBA situations.
>
> So maybe the right thing to do is to just teach lockdep about "lock
> protection locks". That would have solved the multi-queue issues for
> networking too - all the actual network drivers would still have taken
> just their single queue lock, but the one case that needs to take all of
> them would have taken a separate top-level lock first.
>
> Never mind that the multi-queue locks were always taken in the same order:
> it's never wrong to just have some top-level serialization, and anybody
> who needs to take <n> locks might as well do <n+1>, because they sure as
> hell aren't going to be on _any_ fastpaths.
>
> So the simplest solution really sounds like just teaching lockdep about
> that one special case. It's not "nesting" exactly, although it's obviously
> related to it.

Do as Linus suggested. The lock protection lock is called nest_lock.

Note that we still have the MAX_LOCK_DEPTH (48) limit to consider, so anything
that spills that it still up shit creek.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 19 insertions, 17 deletions

diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index e431d1d6eaf3..93a8cc02a033 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -211,6 +211,7 @@ struct held_lock {
 	u64				prev_chain_key;
 	unsigned long			acquire_ip;
 	struct lockdep_map		*instance;
+	struct lockdep_map		*nest_lock;
 #ifdef CONFIG_LOCK_STAT
 	u64 				waittime_stamp;
 	u64				holdtime_stamp;
@@ -297,7 +298,8 @@ extern void lockdep_init_map(struct lockdep_map *lock, const char *name,
  *   2: full validation
  */
 extern void lock_acquire(struct lockdep_map *lock, unsigned int subclass,
-			 int trylock, int read, int check, unsigned long ip);
+			 int trylock, int read, int check,
+			 struct lockdep_map *nest_lock, unsigned long ip);
 
 extern void lock_release(struct lockdep_map *lock, int nested,
 			 unsigned long ip);
@@ -319,7 +321,7 @@ static inline void lockdep_on(void)
 {
 }
 
-# define lock_acquire(l, s, t, r, c, i)		do { } while (0)
+# define lock_acquire(l, s, t, r, c, n, i)	do { } while (0)
 # define lock_release(l, n, i)			do { } while (0)
 # define lock_set_subclass(l, s, i)		do { } while (0)
 # define lockdep_init()				do { } while (0)
@@ -407,9 +409,9 @@ static inline void print_irqtrace_events(struct task_struct *curr)
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 # ifdef CONFIG_PROVE_LOCKING
-#  define spin_acquire(l, s, t, i)		lock_acquire(l, s, t, 0, 2, i)
+#  define spin_acquire(l, s, t, i)		lock_acquire(l, s, t, 0, 2, NULL, i)
 # else
-#  define spin_acquire(l, s, t, i)		lock_acquire(l, s, t, 0, 1, i)
+#  define spin_acquire(l, s, t, i)		lock_acquire(l, s, t, 0, 1, NULL, i)
 # endif
 # define spin_release(l, n, i)			lock_release(l, n, i)
 #else
@@ -419,11 +421,11 @@ static inline void print_irqtrace_events(struct task_struct *curr)
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 # ifdef CONFIG_PROVE_LOCKING
-#  define rwlock_acquire(l, s, t, i)		lock_acquire(l, s, t, 0, 2, i)
-#  define rwlock_acquire_read(l, s, t, i)	lock_acquire(l, s, t, 2, 2, i)
+#  define rwlock_acquire(l, s, t, i)		lock_acquire(l, s, t, 0, 2, NULL, i)
+#  define rwlock_acquire_read(l, s, t, i)	lock_acquire(l, s, t, 2, 2, NULL, i)
 # else
-#  define rwlock_acquire(l, s, t, i)		lock_acquire(l, s, t, 0, 1, i)
-#  define rwlock_acquire_read(l, s, t, i)	lock_acquire(l, s, t, 2, 1, i)
+#  define rwlock_acquire(l, s, t, i)		lock_acquire(l, s, t, 0, 1, NULL, i)
+#  define rwlock_acquire_read(l, s, t, i)	lock_acquire(l, s, t, 2, 1, NULL, i)
 # endif
 # define rwlock_release(l, n, i)		lock_release(l, n, i)
 #else
@@ -434,9 +436,9 @@ static inline void print_irqtrace_events(struct task_struct *curr)
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 # ifdef CONFIG_PROVE_LOCKING
-#  define mutex_acquire(l, s, t, i)		lock_acquire(l, s, t, 0, 2, i)
+#  define mutex_acquire(l, s, t, i)		lock_acquire(l, s, t, 0, 2, NULL, i)
 # else
-#  define mutex_acquire(l, s, t, i)		lock_acquire(l, s, t, 0, 1, i)
+#  define mutex_acquire(l, s, t, i)		lock_acquire(l, s, t, 0, 1, NULL, i)
 # endif
 # define mutex_release(l, n, i)			lock_release(l, n, i)
 #else
@@ -446,11 +448,11 @@ static inline void print_irqtrace_events(struct task_struct *curr)
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 # ifdef CONFIG_PROVE_LOCKING
-#  define rwsem_acquire(l, s, t, i)		lock_acquire(l, s, t, 0, 2, i)
-#  define rwsem_acquire_read(l, s, t, i)	lock_acquire(l, s, t, 1, 2, i)
+#  define rwsem_acquire(l, s, t, i)		lock_acquire(l, s, t, 0, 2, NULL, i)
+#  define rwsem_acquire_read(l, s, t, i)	lock_acquire(l, s, t, 1, 2, NULL, i)
 # else
-#  define rwsem_acquire(l, s, t, i)		lock_acquire(l, s, t, 0, 1, i)
-#  define rwsem_acquire_read(l, s, t, i)	lock_acquire(l, s, t, 1, 1, i)
+#  define rwsem_acquire(l, s, t, i)		lock_acquire(l, s, t, 0, 1, NULL, i)
+#  define rwsem_acquire_read(l, s, t, i)	lock_acquire(l, s, t, 1, 1, NULL, i)
 # endif
 # define rwsem_release(l, n, i)			lock_release(l, n, i)
 #else
@@ -461,9 +463,9 @@ static inline void print_irqtrace_events(struct task_struct *curr)
 
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 # ifdef CONFIG_PROVE_LOCKING
-#  define map_acquire(l)		lock_acquire(l, 0, 0, 0, 2, _THIS_IP_)
+#  define map_acquire(l)		lock_acquire(l, 0, 0, 0, 2, NULL, _THIS_IP_)
 # else
-#  define map_acquire(l)		lock_acquire(l, 0, 0, 0, 1, _THIS_IP_)
+#  define map_acquire(l)		lock_acquire(l, 0, 0, 0, 1, NULL, _THIS_IP_)
 # endif
 # define map_release(l)			lock_release(l, 1, _THIS_IP_)
 #else
diff --git a/include/linux/rcuclassic.h b/include/linux/rcuclassic.h
index 8c774905dcfe..4ab843622727 100644
--- a/include/linux/rcuclassic.h
+++ b/include/linux/rcuclassic.h
@@ -117,7 +117,7 @@ extern int rcu_needs_cpu(int cpu);
 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 extern struct lockdep_map rcu_lock_map;
 # define rcu_read_acquire()	\
-			lock_acquire(&rcu_lock_map, 0, 0, 2, 1, _THIS_IP_)
+			lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
 # define rcu_read_release()	lock_release(&rcu_lock_map, 1, _THIS_IP_)
 #else
 # define rcu_read_acquire()	do { } while (0)