[PATCH] mutex: make mutex_lock_nested an inline function
peterz at infradead.org
Wed Oct 14 06:47:21 PDT 2015
On Wed, Oct 14, 2015 at 01:36:24PM +0100, Mark Brown wrote:
> Sure, but I don't really expect to have to trawl the implementation of
> an API to find out about this sort of thing (I hadn't even been aware
I more like view header files as 'documentation' and c files as
> that the subclasses were required to be small positive integers, never
> mind needing to check what the limit was). I think the main place I'd
> have expected to see it was in lockdep-design.txt or somewhere near
Oh, you're one of them people that actually looks in Documentation/.
> The other big one that came up recently was that lockdep apparently
> works out what a class is by looking at the point of allocation which
> causes a lot of problems for regmap since it makes all regmap locks look
> like a single class. That's fixed now by explicitly allocating a class
> per regmap with some macro magic but it was a bit of a surprise. The
> documentation doesn't make this obvious.
Yes, Documentation/locking/lockdep-design.txt needs help -- I'd even
forgotten we had it.
Does the below work for you?
Documentation/locking/lockdep-design.txt | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/Documentation/locking/lockdep-design.txt b/Documentation/locking/lockdep-design.txt
index 5001280e9d82..e8e9ad4e6f5e 100644
@@ -24,6 +24,10 @@ a lock-class is used for the first time after bootup it gets registered,
and all subsequent uses of that lock-class will be attached to this
+A class is typically associated with a lock's initialisation site; although
+its possible to explicitly initialize a lock with a different class key --
+such class keys much come from static storage.
@@ -165,6 +169,10 @@ partition.
The validator treats a lock that is taken in such a nested fashion as a
separate (sub)class for the purposes of validation.
+Since lock classes are associated with static addresses, the size of struct
+lock_class_key determines the amount of sub classes that are possible --
+currently set to 8.
Note: When changing code to use the _nested() primitives, be careful and
check really thoroughly that the hierarchy is correctly mapped; otherwise
you can get false positives or false negatives.
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