linux-kernel - Re: [PATCH v5 17/36] locking/rwsem: Support Clang's context analysis

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Message-ID: <CANpmjNMAGYeFK-jYafSihmA+T7wi3zC8Sb4fJ+ZjzDK5jGuMvQ@mail.gmail.com>
Date: Sat, 20 Dec 2025 13:52:13 +0100
From: Marco Elver <elver@...gle.com>
To: Bart Van Assche <bvanassche@....org>
Cc: Peter Zijlstra <peterz@...radead.org>, Boqun Feng <boqun.feng@...il.com>, 
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Subject: Re: [PATCH v5 17/36] locking/rwsem: Support Clang's context analysis

On Fri, 19 Dec 2025 at 21:55, 'Bart Van Assche' via kasan-dev
<kasan-dev@...glegroups.com> wrote:
>
> On 12/19/25 7:40 AM, Marco Elver wrote:
> >   static inline void rwsem_assert_held_nolockdep(const struct rw_semaphore *sem)
> > +     __assumes_ctx_lock(sem)
> >   {
> >       WARN_ON(atomic_long_read(&sem->count) == RWSEM_UNLOCKED_VALUE);
> >   }
> >
> >   static inline void rwsem_assert_held_write_nolockdep(const struct rw_semaphore *sem)
> > +     __assumes_ctx_lock(sem)
> >   {
> >       WARN_ON(!(atomic_long_read(&sem->count) & RWSEM_WRITER_LOCKED));
> >   }
> > @@ -119,6 +121,7 @@ do {                                                              \
> >       static struct lock_class_key __key;                     \
> >                                                               \
> >       __init_rwsem((sem), #sem, &__key);                      \
> > +     __assume_ctx_lock(sem);                                 \
> >   } while (0)
>
> Just like as for lockdep.h, I think that the above annotations should be
> changed into __must_hold().

My point is the same: we use it to delegate to dynamic analysis where
we reach the limits of static analysis, to avoid false positives [1].
Code should apply __must_hold() or __guarded_by() to called or
protected variables respectively, which is both cleaner and the
idiomatic way to use all this.

[1] https://lore.kernel.org/all/CANpmjNPp6Gkz3rdaD0V7EkPrm60sA5tPpw+m8Xg3u8MTXuc2mg@mail.gmail.com/