linux-kernel - Re: [PATCH] cleanup: Fix unused guard error function with DEFINE_CLASS_IS_COND

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Message-ID: <aJKH4PlYXSuBua4_@smile.fi.intel.com>
Date: Wed, 6 Aug 2025 01:38:24 +0300
From: Andy Shevchenko <andriy.shevchenko@...el.com>
To: Dan Williams <dan.j.williams@...el.com>
Cc: dave.jiang@...el.com, linux-kernel@...r.kernel.org,
	linux-cxl@...r.kernel.org, Nathan Chancellor <nathan@...nel.org>,
	"Peter Zijlstra (Intel)" <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	David Lechner <dlechner@...libre.com>,
	Jonathan Cameron <jonathan.cameron@...wei.com>
Subject: Re: [PATCH] cleanup: Fix unused guard error function with
 DEFINE_CLASS_IS_COND_GUARD

On Mon, Aug 04, 2025 at 03:09:54PM -0700, Dan Williams wrote:
> Andy reports that the "lock_timer" scheme in kernel/time/posix-timers.c,
> with its custom usage of DEFINE_CLASS_IS_COND_GUARD(), results in:
> 
> kernel/time/posix-timers.c:89:1: error: unused function 'class_lock_timer_lock_err' [-Werror,-Wunused-function]
>    89 | DEFINE_CLASS_IS_COND_GUARD(lock_timer);
> 
> ...with a clang W=1 build. Per Nathan, clang catches unused "static inline"
> functions in C files since commit 6863f5643dd7 ("kbuild: allow Clang to
> find unused static inline functions for W=1 build").
> 
> There are 2 ways to solve this, either mark the class_##_lock_err()
> function as __maybe_unused, or make sure class_##_lock_err() *is* used /
> gets called to disposition the lock status.
> 
> At present __lock_timer() only indicates failure with a NULL __guard_ptr().
> However, one could imagine that __lock_timer(), or some other custom
> conditional locking primitive, wants to pass an ERR_PTR() to indicate the
> reason for the lock acquisition failure.
> 
> Update __scoped_cond_guard() to check for ERR_PTR() in addition to NULL
> @scope values. This allows __lock_timer(), or another open coded
> DEFINE_CLASS_IS_COND_GUARD() user, to switch to passing an ERR_PTR() in the
> future. In the meantime, this just silences the warning.

Hmm... It seems fixes the timer case, but left others still fail:

drivers/pwm/core.c:54:1: error: unused function 'class_pwmchip_lock_err' [-Werror,-Wunused-function]
   54 | DEFINE_GUARD(pwmchip, struct pwm_chip *, pwmchip_lock(_T), pwmchip_unlock(_T))
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
include/linux/cleanup.h:380:2: note: expanded from macro 'DEFINE_GUARD'
  380 |         DEFINE_CLASS_IS_GUARD(_name)
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
include/linux/cleanup.h:372:2: note: expanded from macro 'DEFINE_CLASS_IS_GUARD'
  372 |         __DEFINE_GUARD_LOCK_PTR(_name, _T)
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
include/linux/cleanup.h:358:20: note: expanded from macro '__DEFINE_GUARD_LOCK_PTR'
  358 |         static inline int class_##_name##_lock_err(class_##_name##_t *_T)   \
      |                           ^~~~~~~~~~~~~~~~~~~~~~~~
<scratch space>:81:1: note: expanded from here
   81 | class_pwmchip_lock_err
      | ^~~~~~~~~~~~~~~~~~~~~~
1 error generated.

fs/namespace.c:1782:1: error: unused function 'class_namespace_lock_lock_err' [-Werror,-Wunused-function]
  1782 | DEFINE_GUARD(namespace_lock, struct rw_semaphore *, namespace_lock(), namespace_unlock())
       | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
include/linux/cleanup.h:380:2: note: expanded from macro 'DEFINE_GUARD'
  380 |         DEFINE_CLASS_IS_GUARD(_name)
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
include/linux/cleanup.h:372:2: note: expanded from macro 'DEFINE_CLASS_IS_GUARD'
  372 |         __DEFINE_GUARD_LOCK_PTR(_name, _T)
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
include/linux/cleanup.h:358:20: note: expanded from macro '__DEFINE_GUARD_LOCK_PTR'
  358 |         static inline int class_##_name##_lock_err(class_##_name##_t *_T)   \
      |                           ^~~~~~~~~~~~~~~~~~~~~~~~
<scratch space>:15:1: note: expanded from here
   15 | class_namespace_lock_lock_err
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

These I have and I dunno how many more can be detected with allyesconfig and/or
allmodconfig on all possible architectures...

-- 
With Best Regards,
Andy Shevchenko