Re: [peterz-queue:locking/core 10/10] kernel/futex/core.c:982:1: warning: spinlock 'atomic ? __u.__val : q->lock_ptr' is still held at the end of function

[Peter Zijlstra <peterz@infradead.org>]

On Thu, Jan 22, 2026 at 10:30:28AM +0800, kernel test robot wrote:
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git locking/core
> head:   33d9e7fdf9c17417347d1f06ddebaf25f21ab62a
> commit: 33d9e7fdf9c17417347d1f06ddebaf25f21ab62a [10/10] futex: Convert to compiler context analysis
> config: arm64-randconfig-001-20260122 (https://download.01.org/0day-ci/archive/20260122/202601221040.TeM0ihff-lkp@intel.com/config)
> compiler: clang version 22.0.0git (https://github.com/llvm/llvm-project 9b8addffa70cee5b2acc5454712d9cf78ce45710)
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260122/202601221040.TeM0ihff-lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot <lkp@intel.com>
> | Closes: https://lore.kernel.org/oe-kbuild-all/202601221040.TeM0ihff-lkp@intel.com/
> 
> All warnings (new ones prefixed by >>):
> 
> >> kernel/futex/core.c:982:1: warning: spinlock 'atomic ? __u.__val : q->lock_ptr' is still held at the end of function [-Wthread-safety-analysis]
>      982 | }
>          | ^
>    kernel/futex/core.c:976:2: note: spinlock acquired here
>      976 |         spin_lock(lock_ptr);
>          |         ^
> >> kernel/futex/core.c:982:1: warning: expecting spinlock 'q->lock_ptr' to be held at the end of function [-Wthread-safety-analysis]
>      982 | }
>          | ^
>    kernel/futex/core.c:966:6: note: spinlock acquired here
>      966 | void futex_q_lockptr_lock(struct futex_q *q)
>          |      ^
>    2 warnings generated.

Urgh, this is the arm64 READ_ONCE() confusing the thing. It can't see
through that mess and realize: lockptr == q->lock_ptr.

Marco, any suggestion how to best fix that?