Re: [PATCH 3/5] seqlock: introduce seqprop_lock/unlock

Alexey Gladkov
2023-09-15T18:26:29Z

On Wed, Sep 13, 2023 at 05:50:00PM +0200, Oleg Nesterov wrote:
> which can be used to take/release the corresponding lock.
>
> Thanks to the previous patch, it is trivial to pass 2 arguments to
> the new __seqprop_##lockname##_lock/unlock "methods", plus we do not
> loose the type info and thus the new seqprop's are "type safe".
>
> So for example
>
> void func(seqcount_rwlock_t *s, rwlock_t *l)
> {
> seqprop_lock(s, l);
> }
>
> happily compiles, but this one
>
> void func(seqcount_rwlock_t *s, spinlock_t *l)
> {
> seqprop_lock(s, l);
> }
>
> doesn't.
>
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>
> ---
> include/linux/seqlock.h | 21 +++++++++++++++++++++
> 1 file changed, 21 insertions(+)
>
> diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
> index 41e36f8afad4..9831683a0102 100644
> --- a/include/linux/seqlock.h
> +++ b/include/linux/seqlock.h
> @@ -241,6 +241,21 @@ static __always_inline void \
> __seqprop_##lockname##_assert(const seqcount_##lockname##_t *s) \
> { \
> __SEQ_LOCK(lockdep_assert_held(s->lock)); \
> +} \
> + \
> +static __always_inline void \
> +__seqprop_##lockname##_lock(seqcount_##lockname##_t *s, \
> + locktype *lock) \
> +{ \
> + __SEQ_LOCK(WARN_ON_ONCE(s->lock != lock)); \
> + lockbase##_lock(lock); \
> +} \
> + \
> +static __always_inline void \
> +__seqprop_##lockname##_unlock(seqcount_##lockname##_t *s, \
> + locktype *lock) \
> +{ \
> + lockbase##_unlock(lock); \
> }

Why are you creating a new method with an unused argument s ?

>
> /*
> @@ -306,6 +321,12 @@ SEQCOUNT_LOCKNAME(mutex, struct mutex, true, mutex)
> #define seqprop_preemptible(s) __seqprop(s, preemptible)(s)
> #define seqprop_assert(s) __seqprop(s, assert)(s)
>
> +/* seqcount_t doesn't have these methods */
> +static inline void __seqprop_lock (seqcount_t *s, void *l) { BUILD_BUG(); }
> +static inline void __seqprop_unlock (seqcount_t *s, void *l) { BUILD_BUG(); }
> +#define seqprop_lock(s, l) __seqprop(s, lock)(s, l)
> +#define seqprop_unlock(s, l) __seqprop(s, unlock)(s, l)
> +
> /**
> * __read_seqcount_begin() - begin a seqcount_t read section w/o barrier
> * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
> --
> 2.25.1.362.g51ebf55
>

--
Rgrds, legion