Re: [PATCH 1/3] cleanup: add conditional guard helper

Peter Zijlstra
2024-10-18T11:15:09Z

On Tue, Oct 01, 2024 at 05:30:18PM -0500, David Lechner wrote:
> Add a new if_not_cond_guard() macro to cleanup.h for handling
> conditional guards such as mutext_trylock().
>
> This is more ergonomic than scoped_cond_guard() for most use cases.
> Instead of hiding the error handling statement in the macro args, it
> works like a normal if statement and allow the error path to be indented
> while the normal code flow path is not indented. And it avoid unwanted
> side-effect from hidden for loop in scoped_cond_guard().
>
> Signed-off-by: David Lechner <dlechner@baylibre.com>
> ---
> include/linux/cleanup.h | 11 +++++++++++
> 1 file changed, 11 insertions(+)
>
> diff --git a/include/linux/cleanup.h b/include/linux/cleanup.h
> index 038b2d523bf8..682bb3fadfc9 100644
> --- a/include/linux/cleanup.h
> +++ b/include/linux/cleanup.h
> @@ -273,6 +273,10 @@ static inline class_##_name##_t class_##_name##ext##_constructor(_init_args) \
> * an anonymous instance of the (guard) class, not recommended for
> * conditional locks.
> *
> + * if_not_cond_guard(name, args...) { <error handling> }:
> + * convenience macro for conditional guards that calls the statement that
> + * follows only if the lock was not acquired (typically an error return).
> + *
> * scoped_guard (name, args...) { }:
> * similar to CLASS(name, scope)(args), except the variable (with the
> * explicit name 'scope') is declard in a for-loop such that its scope is
> @@ -304,6 +308,13 @@ static inline class_##_name##_t class_##_name##ext##_constructor(_init_args) \
>
> #define __guard_ptr(_name) class_##_name##_lock_ptr
>
> +#define __if_not_cond_guard(_name, _id, args...) \
> + CLASS(_name, _id)(args); \
> + if (!__guard_ptr(_name)(&_id))
> +
> +#define if_not_cond_guard(_name, args...) \
> + __if_not_cond_guard(_name, __UNIQUE_ID(guard), args)
> +
> #define scoped_guard(_name, args...) \
> for (CLASS(_name, scope)(args), \
> *done = NULL; __guard_ptr(_name)(&scope) && !done; done = (void *)1)

So if I stick this on top of:

https://lkml.kernel.org/r/20241011121535.28049-1-przemyslaw.kitszel@intel.com

then I can add the below:

--- a/include/linux/cleanup.h
+++ b/include/linux/cleanup.h
@@ -277,6 +277,8 @@ static inline class_##_name##_t class_##
* convenience macro for conditional guards that calls the statement that
* follows only if the lock was not acquired (typically an error return).
*
+ * Only for conditional locks.
+ *
* scoped_guard (name, args...) { }:
* similar to CLASS(name, scope)(args), except the variable (with the
* explicit name 'scope') is declard in a for-loop such that its scope is
@@ -290,7 +292,6 @@ static inline class_##_name##_t class_##
* acquire fails.
*
* Only for conditional locks.
- *
*/

#define __DEFINE_CLASS_IS_CONDITIONAL(_name, _is_cond) \
@@ -342,6 +343,7 @@ _label: \
__UNIQUE_ID(label), args)

#define __if_not_guard(_name, _id, args...) \
+ BUILD_BUG_ON(!__is_cond_ptr(_name)); \
CLASS(_name, _id)(args); \
if (!__guard_ptr(_name)(&_id))

That make sense to people?

I've queued these two patches:

git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git locking/core

But lacking if_not_guard() users, the robot isn't really going to give
me much feedback there, I suppose...