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 [thread overview]
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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next prev parent reply other threads:[~2015-09-12 5:47 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-09-10 0:57 [rcu] kernel BUG at include/linux/pagemap.h:149! 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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