Re: [RFC][PATCH 1/2] locking: Introduce __cleanup__ based guards

[Waiman Long]

On 5/26/23 11:05, Peter Zijlstra wrote:
> Use __attribute__((__cleanup__(func))) to buid various guards:
>
>   - ptr_guard()
>   - void_guard() / void_scope()
>   - lock_guard() / lock_scope()
>   - double_lock_guard() / double_lock_scope()
>
> Where the _guard thingies are variables with scope-based cleanup and
> the _scope thingies are basically do-once for-loops with the same.
>
> The CPP is rather impenetrable -- but I'll attempt to write proper
> comments if/when people think this is worth pursuing.
>
> Actual usage in the next patch
>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> ---
>   include/linux/compiler_attributes.h |    2
>   include/linux/irqflags.h            |    7 ++
>   include/linux/guards.h          |  118 ++++++++++++++++++++++++++++++++++++
>   include/linux/mutex.h               |    5 +
>   include/linux/preempt.h             |    4 +
>   include/linux/rcupdate.h            |    3
>   include/linux/sched/task.h          |    2
>   include/linux/spinlock.h            |   23 +++++++
>   8 files changed, 164 insertions(+)

That is an interesting idea and may help to simplify some of the common 
code patterns that we have in the kernel. The macros are a bit hard to 
read and understand though I thought I got a rough idea of what they are 
trying to do.

BTW, do we have a use case for double_lock_guard/double_lock_scope? I 
can envision a nested lock_scope inside a lock_scope, but taking 2 auto 
locks of the same type at init time and then unlock them at exit just 
doesn't make sense to me.

Cheers,
Longman