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> Concrete example: in Rust, locking a mutex returns a handle that lets you access the data protected by the mutex, and the mutex is unlocked when the handle is dropped.

This is how it works in the kernel on the C side, too. Usually by using guard/scoped_guard which wrap the generic mutexes with some RAII.

yencabulator a day ago [ - ]

Interestingly enough, this is the only mention of scoped_guard in Documentation/. I will definitely argue that (that part of) Rust is way more approachable.

  Using device-managed and cleanup.h constructs
  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
  
  Netdev remains skeptical about promises of all "auto-cleanup" APIs,
  including even ``devm_`` helpers, historically. They are not the preferred
  style of implementation, merely an acceptable one.
  
  Use of ``guard()`` is discouraged within any function longer than 20 lines,
  ``scoped_guard()`` is considered more readable. Using normal lock/unlock is
  still (weakly) preferred.
  
  Low level cleanup constructs (such as ``__free()``) can be used when building
  APIs and helpers, especially scoped iterators. However, direct use of
  ``__free()`` within networking core and drivers is discouraged.
  Similar guidance applies to declaring variables mid-function.

yencabulator a day ago [ - ]

  #define guard(_name) \
          CLASS(_name, __UNIQUE_ID(guard))

  #define CLASS(_name, var)                                               \
          class_##_name##_t var __cleanup(class_##_name##_destructor) =   \
                  class_##_name##_constructor

  #define __UNIQUE_ID(prefix) __PASTE(__PASTE(__UNIQUE_ID_, prefix), __COUNTER__)

Yeah Rust wins this one hands down, without breaking a sweat, and without really even noticing there was a competition.