linux-kernel - Re: [PATCH v2 09/13] locking/percpu-rwsem: Add percpu_is_write_locked() and percpu_is_read

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Date:   Tue, 28 Jun 2022 16:44:41 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Marco Elver <elver@...gle.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <frederic@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev@...ts.ozlabs.org, linux-perf-users@...r.kernel.org,
        x86@...nel.org, linux-sh@...r.kernel.org,
        kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 09/13] locking/percpu-rwsem: Add percpu_is_write_locked()
 and percpu_is_read_locked()

On Tue, 28 Jun 2022 at 11:59, Marco Elver <elver@...gle.com> wrote:
>
> Implement simple accessors to probe percpu-rwsem's locked state:
> percpu_is_write_locked(), percpu_is_read_locked().
>
> Signed-off-by: Marco Elver <elver@...gle.com>

Reviewed-by: Dmitry Vyukov <dvyukov@...gle.com>

> ---
> v2:
> * New patch.
> ---
>  include/linux/percpu-rwsem.h  | 6 ++++++
>  kernel/locking/percpu-rwsem.c | 6 ++++++
>  2 files changed, 12 insertions(+)
>
> diff --git a/include/linux/percpu-rwsem.h b/include/linux/percpu-rwsem.h
> index 5fda40f97fe9..36b942b67b7d 100644
> --- a/include/linux/percpu-rwsem.h
> +++ b/include/linux/percpu-rwsem.h
> @@ -121,9 +121,15 @@ static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
>         preempt_enable();
>  }
>
> +extern bool percpu_is_read_locked(struct percpu_rw_semaphore *);
>  extern void percpu_down_write(struct percpu_rw_semaphore *);
>  extern void percpu_up_write(struct percpu_rw_semaphore *);
>
> +static inline bool percpu_is_write_locked(struct percpu_rw_semaphore *sem)
> +{
> +       return atomic_read(&sem->block);
> +}
> +
>  extern int __percpu_init_rwsem(struct percpu_rw_semaphore *,
>                                 const char *, struct lock_class_key *);
>
> diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
> index 5fe4c5495ba3..213d114fb025 100644
> --- a/kernel/locking/percpu-rwsem.c
> +++ b/kernel/locking/percpu-rwsem.c
> @@ -192,6 +192,12 @@ EXPORT_SYMBOL_GPL(__percpu_down_read);
>         __sum;                                                          \
>  })
>
> +bool percpu_is_read_locked(struct percpu_rw_semaphore *sem)
> +{
> +       return per_cpu_sum(*sem->read_count) != 0;
> +}
> +EXPORT_SYMBOL_GPL(percpu_is_read_locked);
> +
>  /*
>   * Return true if the modular sum of the sem->read_count per-CPU variable is
>   * zero.  If this sum is zero, then it is stable due to the fact that if any
> --
> 2.37.0.rc0.161.g10f37bed90-goog
>