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From: Boqun Feng <boqun.feng@gmail.com>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>, LKP <lkp@01.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Frederic Weisbecker <fweisbec@gmail.com>
Subject: Re: [rcu] kernel BUG at include/linux/pagemap.h:149!
Date: Sat, 12 Sep 2015 13:46:37 +0800
Message-ID: <20150912054624.GF1521@fixme-laptop.cn.ibm.com> (raw)
In-Reply-To: <20150911215937.GH4029@linux.vnet.ibm.com>


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On Fri, Sep 11, 2015 at 02:59:37PM -0700, Paul E. McKenney wrote:
> 
> Queued for v4.4, thank you!  Please see below for updated commit log,
> and please let me know if there are any problems with it.
> 

Looks great to me! Thank you ;-)

Regards,
Boqun

> ------------------------------------------------------------------------
> 
>     rcu: Don't disable preemption for Tiny and Tree RCU readers
>     
>     Because preempt_disable() maps to barrier() for non-debug builds,
>     it forces the compiler to spill and reload registers.  Because Tree
>     RCU and Tiny RCU now only appear in CONFIG_PREEMPT=n builds, these
>     barrier() instances generate needless extra code for each instance of
>     rcu_read_lock() and rcu_read_unlock().  This extra code slows down Tree
>     RCU and bloats Tiny RCU.
>     
>     This commit therefore removes the preempt_disable() and preempt_enable()
>     from the non-preemptible implementations of __rcu_read_lock() and
>     __rcu_read_unlock(), respectively.  However, for debug purposes,
>     preempt_disable() and preempt_enable() are still invoked if
>     CONFIG_PREEMPT_COUNT=y, because this allows detection of sleeping inside
>     atomic sections in non-preemptible kernels.
>     
>     This is based on an earlier patch by Paul E. McKenney, fixing
>     a bug encountered in kernels built with CONFIG_PREEMPT=n and
>     CONFIG_PREEMPT_COUNT=y.
>     
>     Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
>     Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> 
> diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> index d63bb77dab35..6c3ceceb6148 100644
> --- a/include/linux/rcupdate.h
> +++ b/include/linux/rcupdate.h
> @@ -297,12 +297,14 @@ void synchronize_rcu(void);
>  
>  static inline void __rcu_read_lock(void)
>  {
> -	preempt_disable();
> +	if (IS_ENABLED(CONFIG_PREEMPT_COUNT))
> +		preempt_disable();
>  }
>  
>  static inline void __rcu_read_unlock(void)
>  {
> -	preempt_enable();
> +	if (IS_ENABLED(CONFIG_PREEMPT_COUNT))
> +		preempt_enable();
>  }
>  
>  static inline void synchronize_rcu(void)
> diff --git a/include/linux/rcutiny.h b/include/linux/rcutiny.h
> index c8a0722f77ea..4c1aaf9cce7b 100644
> --- a/include/linux/rcutiny.h
> +++ b/include/linux/rcutiny.h
> @@ -216,6 +216,7 @@ static inline bool rcu_is_watching(void)
>  
>  static inline void rcu_all_qs(void)
>  {
> +	barrier(); /* Avoid RCU read-side critical sections leaking across. */
>  }
>  
>  #endif /* __LINUX_RCUTINY_H */
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index ce43fac5ff91..b4882f8b8a9e 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -337,12 +337,14 @@ static void rcu_momentary_dyntick_idle(void)
>   */
>  void rcu_note_context_switch(void)
>  {
> +	barrier(); /* Avoid RCU read-side critical sections leaking down. */
>  	trace_rcu_utilization(TPS("Start context switch"));
>  	rcu_sched_qs();
>  	rcu_preempt_note_context_switch();
>  	if (unlikely(raw_cpu_read(rcu_sched_qs_mask)))
>  		rcu_momentary_dyntick_idle();
>  	trace_rcu_utilization(TPS("End context switch"));
> +	barrier(); /* Avoid RCU read-side critical sections leaking up. */
>  }
>  EXPORT_SYMBOL_GPL(rcu_note_context_switch);
>  
> @@ -353,12 +355,19 @@ EXPORT_SYMBOL_GPL(rcu_note_context_switch);
>   * RCU flavors in desperate need of a quiescent state, which will normally
>   * be none of them).  Either way, do a lightweight quiescent state for
>   * all RCU flavors.
> + *
> + * The barrier() calls are redundant in the common case when this is
> + * called externally, but just in case this is called from within this
> + * file.
> + *
>   */
>  void rcu_all_qs(void)
>  {
> +	barrier(); /* Avoid RCU read-side critical sections leaking down. */
>  	if (unlikely(raw_cpu_read(rcu_sched_qs_mask)))
>  		rcu_momentary_dyntick_idle();
>  	this_cpu_inc(rcu_qs_ctr);
> +	barrier(); /* Avoid RCU read-side critical sections leaking up. */
>  }
>  EXPORT_SYMBOL_GPL(rcu_all_qs);
>  
> 

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  reply index

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-09-10  0:57 Fengguang Wu
2015-09-10 10:25 ` Boqun Feng
2015-09-10 17:16   ` Paul E. McKenney
2015-09-11  2:19     ` Boqun Feng
     [not found]       ` <CAJzB8QG=1iZW3dQEie6ZSTLv8GZ3YSut0aL1VU7LLmiHQ1B1DQ@mail.gmail.com>
2015-09-11 21:59         ` Paul E. McKenney
2015-09-12  5:46           ` Boqun Feng [this message]
2015-09-21 19:30       ` Frederic Weisbecker
2015-09-21 20:43         ` Paul E. McKenney
2019-06-02  5:56           ` rcu_read_lock lost its compiler barrier Herbert Xu
2019-06-02 20:54             ` Linus Torvalds
2019-06-03  2:46               ` Herbert Xu
2019-06-03  3:47                 ` Paul E. McKenney
2019-06-03  4:01                   ` Herbert Xu
2019-06-03  4:17                     ` Herbert Xu
2019-06-03  7:23                     ` Paul E. McKenney
2019-06-03  8:42                       ` Paul E. McKenney
2019-06-03 15:26                         ` David Laight
2019-06-03 15:40                           ` Linus Torvalds
2019-06-03  5:26                   ` Herbert Xu
2019-06-03  6:42                     ` Boqun Feng
2019-06-03 20:03                       ` Paul E. McKenney
2019-06-04 14:44                         ` Alan Stern
2019-06-04 16:04                           ` Linus Torvalds
2019-06-04 17:00                             ` Alan Stern
2019-06-04 17:29                               ` Linus Torvalds
2019-06-07 14:09                             ` inet: frags: Turn fqdir->dead into an int for old Alphas Herbert Xu
2019-06-07 15:26                               ` Eric Dumazet
2019-06-07 15:32                                 ` Herbert Xu
2019-06-07 16:13                                   ` Eric Dumazet
2019-06-07 16:19                                 ` Linus Torvalds
2019-06-08 15:27                                   ` Paul E. McKenney
2019-06-08 17:42                                     ` Linus Torvalds
2019-06-08 17:50                                       ` Linus Torvalds
2019-06-08 18:50                                         ` Paul E. McKenney
2019-06-08 18:14                                       ` Paul E. McKenney
2019-06-06  4:51                           ` rcu_read_lock lost its compiler barrier Herbert Xu
2019-06-06  6:05                             ` Paul E. McKenney
2019-06-06  6:14                               ` Herbert Xu
2019-06-06  9:06                                 ` Paul E. McKenney
2019-06-06  9:28                                   ` Herbert Xu
2019-06-06 10:58                                     ` Paul E. McKenney
2019-06-06 13:38                                       ` Herbert Xu
2019-06-06 13:48                                         ` Paul E. McKenney
2019-06-06  8:16                           ` Andrea Parri
2019-06-06 14:19                             ` Alan Stern
2019-06-08 15:19                               ` Paul E. McKenney
2019-06-08 15:56                                 ` Alan Stern
2019-06-08 16:31                                   ` Paul E. McKenney
2019-06-03  9:35                     ` Paul E. McKenney
2019-06-06  8:38                 ` Andrea Parri
2019-06-06  9:32                   ` Herbert Xu
2019-06-03  0:06             ` Paul E. McKenney
2019-06-03  3:03               ` Herbert Xu
2019-06-03  9:27                 ` Paul E. McKenney
2019-06-03 15:55                 ` Linus Torvalds
2019-06-03 16:07                   ` Linus Torvalds
2019-06-03 19:53                     ` Paul E. McKenney
2019-06-03 20:24                       ` Linus Torvalds
2019-06-04 21:14                         ` Paul E. McKenney
2019-06-05  2:21                           ` Herbert Xu
2019-06-05  3:30                             ` Paul E. McKenney
2019-06-06  4:37                               ` Herbert Xu

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