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>
diff --git a/include/linux/lockdep.h b/include/linux/lockdep.h
index e431d1d..93a8cc0 100644
--- a/include/linux/lockdep.h
+++ b/include/linux/lockdep.h
@@ -211,6 +211,7 @@
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 @@
* 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 @@
{
}
-# 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 @@
#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 @@
#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 @@
#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 @@
#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 @@
#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