linux-kernel - Re: [PATCH RT v3 1/5] rcu: Acquire RCU lock when disabling BHs

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Message-ID: <20190917074456.yj7t3wdwuhn3zcng@linutronix.de>
Date:   Tue, 17 Sep 2019 09:44:57 +0200
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     Scott Wood <swood@...hat.com>
Cc:     linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org,
        "Paul E . McKenney" <paulmck@...ux.ibm.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Steven Rostedt <rostedt@...dmis.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Clark Williams <williams@...hat.com>
Subject: Re: [PATCH RT v3 1/5] rcu: Acquire RCU lock when disabling BHs

On 2019-09-11 17:57:25 [+0100], Scott Wood wrote:
> index 388ace315f32..9ce7c5006a5e 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -600,6 +600,36 @@ static inline void rcu_read_unlock(void)
>  	rcu_lock_release(&rcu_lock_map); /* Keep acq info for rls diags. */
>  }
>  
> +#ifdef CONFIG_PREEMPT_RT_FULL
> +/*
> + * On RT, local_bh_disable() calls rcu_read_lock() -- no need to
> + * track it twice.
> + */
> +static inline void rcu_bh_lock_acquire(void)
> +{
> +}
> +
> +static inline void rcu_bh_lock_release(void)
> +{
> +}
> +#else
> +static inline void rcu_bh_lock_acquire(void)
> +{
> +	__acquire(RCU_BH);
> +	rcu_lock_acquire(&rcu_bh_lock_map);
> +	RCU_LOCKDEP_WARN(!rcu_is_watching(),
> +			 "rcu_read_lock_bh() used illegally while idle");
> +}
> +
> +static inline void rcu_bh_lock_release(void)
> +{
> +	RCU_LOCKDEP_WARN(!rcu_is_watching(),
> +			 "rcu_read_unlock_bh() used illegally while idle");
> +	rcu_lock_release(&rcu_bh_lock_map);
> +	__release(RCU_BH);
> +}
> +#endif
> +
>  /**
>   * rcu_read_lock_bh() - mark the beginning of an RCU-bh critical section
>   *
> @@ -615,10 +645,7 @@ static inline void rcu_read_unlock(void)
>  static inline void rcu_read_lock_bh(void)
>  {
>  	local_bh_disable();
> -	__acquire(RCU_BH);
> -	rcu_lock_acquire(&rcu_bh_lock_map);
> -	RCU_LOCKDEP_WARN(!rcu_is_watching(),
> -			 "rcu_read_lock_bh() used illegally while idle");
> +	rcu_bh_lock_acquire();
>  }
>  
>  /*

I asked previously why do you need to change rcu_read_lock_bh() and you
replied that you don't remember:
   https://lore.kernel.org/linux-rt-users/b948ec6cccda31925ed8dc123bd0f55423fff3d4.camel@redhat.com/

Did this change?

Sebastian