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From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Josh Triplett <josh@joshtriplett.org>
Cc: linux-kernel@vger.kernel.org, mingo@elte.hu,
	laijs@cn.fujitsu.com, dipankar@in.ibm.com,
	akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca,
	niv@us.ibm.com, tglx@linutronix.de, peterz@infradead.org,
	rostedt@goodmis.org, Valdis.Kletnieks@vt.edu,
	dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com,
	fweisbec@gmail.com, sbw@mit.edu, patches@linaro.org,
	"Paul E. McKenney" <paul.mckenney@linaro.org>
Subject: Re: [PATCH tip/core/rcu 04/15] rcu: Permit RCU_NONIDLE() to be used from interrupt context
Date: Tue, 4 Sep 2012 15:33:50 -0700	[thread overview]
Message-ID: <20120904223350.GQ2593@linux.vnet.ibm.com> (raw)
In-Reply-To: <20120831180052.GB4259@jtriplet-mobl1>

On Fri, Aug 31, 2012 at 11:00:52AM -0700, Josh Triplett wrote:
> On Thu, Aug 30, 2012 at 11:56:17AM -0700, Paul E. McKenney wrote:
> > From: "Paul E. McKenney" <paul.mckenney@linaro.org>
> > 
> > There is a need to use RCU from interrupt context, but either before
> > rcu_irq_enter() is called or after rcu_irq_exit() is called.  If the
> > interrupt occurs from idle, then lockdep-RCU will complain about such
> > uses, as they appear to be illegal uses of RCU from the idle loop.
> > In other environments, RCU_NONIDLE() could be used to properly protect
> > the use of RCU, but RCU_NONIDLE() currently cannot be invoked except
> > from process context.
> > 
> > This commit therefore modifies RCU_NONIDLE() to permit its use more
> > globally.
> > 
> > Reported-by: Steven Rostedt <rostedt@goodmis.org>
> > Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> 
> Something seems wrong about this.  The addition of EXPORT_SYMBOL_GPL
> suggests that such interrupt handlers might live in modules.  In what
> situation might a module interrupt handler get called from the idle
> loop, before rcu_irq_enter or after rcu_irq_exit, and need to know that
> when using RCU?

Drivers can be in modules, in which case their interrupt handlers will
also be in the corresponding module.  I do agree that in most cases,
the irq_enter() and irq_exit() hooks would be invoked by non-module code,
but I do believe that I had to add those exports due to build failures.

Steven will let me know if I am confused on this point.

							Thanx, Paul

> - Josh Triplett
> 
> > ---
> >  include/linux/rcupdate.h |    6 ++----
> >  kernel/rcutiny.c         |    2 ++
> >  kernel/rcutree.c         |    2 ++
> >  3 files changed, 6 insertions(+), 4 deletions(-)
> > 
> > diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h
> > index 115ead2..0fbbd52 100644
> > --- a/include/linux/rcupdate.h
> > +++ b/include/linux/rcupdate.h
> > @@ -210,14 +210,12 @@ extern void exit_rcu(void);
> >   * to nest RCU_NONIDLE() wrappers, but the nesting level is currently
> >   * quite limited.  If deeper nesting is required, it will be necessary
> >   * to adjust DYNTICK_TASK_NESTING_VALUE accordingly.
> > - *
> > - * This macro may be used from process-level code only.
> >   */
> >  #define RCU_NONIDLE(a) \
> >  	do { \
> > -		rcu_idle_exit(); \
> > +		rcu_irq_enter(); \
> >  		do { a; } while (0); \
> > -		rcu_idle_enter(); \
> > +		rcu_irq_exit(); \
> >  	} while (0)
> >  
> >  /*
> > diff --git a/kernel/rcutiny.c b/kernel/rcutiny.c
> > index e4163c5..2e073a2 100644
> > --- a/kernel/rcutiny.c
> > +++ b/kernel/rcutiny.c
> > @@ -115,6 +115,7 @@ void rcu_irq_exit(void)
> >  	rcu_idle_enter_common(newval);
> >  	local_irq_restore(flags);
> >  }
> > +EXPORT_SYMBOL_GPL(rcu_irq_exit);
> >  
> >  /* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcutree.c. */
> >  static void rcu_idle_exit_common(long long oldval)
> > @@ -172,6 +173,7 @@ void rcu_irq_enter(void)
> >  	rcu_idle_exit_common(oldval);
> >  	local_irq_restore(flags);
> >  }
> > +EXPORT_SYMBOL_GPL(rcu_irq_enter);
> >  
> >  #ifdef CONFIG_DEBUG_LOCK_ALLOC
> >  
> > diff --git a/kernel/rcutree.c b/kernel/rcutree.c
> > index f280e54..96b8aff 100644
> > --- a/kernel/rcutree.c
> > +++ b/kernel/rcutree.c
> > @@ -447,6 +447,7 @@ void rcu_irq_exit(void)
> >  		rcu_idle_enter_common(rdtp, oldval);
> >  	local_irq_restore(flags);
> >  }
> > +EXPORT_SYMBOL_GPL(rcu_irq_exit);
> >  
> >  /*
> >   * rcu_idle_exit_common - inform RCU that current CPU is moving away from idle
> > @@ -542,6 +543,7 @@ void rcu_irq_enter(void)
> >  		rcu_idle_exit_common(rdtp, oldval);
> >  	local_irq_restore(flags);
> >  }
> > +EXPORT_SYMBOL_GPL(rcu_irq_enter);
> >  
> >  /**
> >   * rcu_nmi_enter - inform RCU of entry to NMI context
> > -- 
> > 1.7.8
> > 
> 


  reply	other threads:[~2012-09-04 22:34 UTC|newest]

Thread overview: 86+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-08-30 18:56 [PATCH tip/core/rcu 0/15] Miscellaneous fixes Paul E. McKenney
2012-08-30 18:56 ` [PATCH tip/core/rcu 01/15] rcu: Add PROVE_RCU_DELAY to provoke difficult races Paul E. McKenney
2012-08-30 18:56   ` [PATCH tip/core/rcu 02/15] rcu: Pull TINY_RCU dyntick-idle tracing into non-idle region Paul E. McKenney
2012-08-31 16:53     ` Josh Triplett
2012-08-30 18:56   ` [PATCH tip/core/rcu 03/15] rcu: Properly initialize ->boost_tasks on CPU offline Paul E. McKenney
2012-08-31 17:56     ` Josh Triplett
2012-09-06 14:40     ` Peter Zijlstra
2012-09-06 20:58       ` Paul E. McKenney
2012-08-30 18:56   ` [PATCH tip/core/rcu 04/15] rcu: Permit RCU_NONIDLE() to be used from interrupt context Paul E. McKenney
2012-08-31 18:00     ` Josh Triplett
2012-09-04 22:33       ` Paul E. McKenney [this message]
2012-09-04 22:48         ` Josh Triplett
2012-09-04 22:51         ` Steven Rostedt
2012-09-04 23:08           ` Josh Triplett
2012-09-04 23:23             ` Steven Rostedt
2012-09-04 23:33               ` Josh Triplett
2012-09-04 23:43                 ` Paul E. McKenney
2012-09-06 18:54                   ` Josh Triplett
2012-09-06 19:54                     ` Steven Rostedt
2012-09-07  6:09                       ` Josh Triplett
2012-09-07 14:24                         ` Paul E. McKenney
2012-09-07 14:47                           ` Josh Triplett
2012-09-07 15:16                             ` Steven Rostedt
2012-09-12  1:07                               ` Paul E. McKenney
2012-09-12 14:13                                 ` Steven Rostedt
2012-09-12 15:03                                   ` Paul E. McKenney
2012-09-12 15:18                                     ` Steven Rostedt
2012-09-12 16:57                                       ` Paul E. McKenney
2012-09-04 23:46                 ` Steven Rostedt
2012-09-05  0:42                   ` Josh Triplett
2012-09-05  6:23                   ` [PATCH] trace: Don't declare trace_*_rcuidle functions in modules Josh Triplett
2012-09-05 14:26                     ` Mathieu Desnoyers
2012-09-05 16:36                     ` Paul E. McKenney
2012-09-06 19:49                     ` Steven Rostedt
2012-09-14  6:07                     ` [tip:core/rcu] trace: Don' t " tip-bot for Josh Triplett
2012-09-04 23:14           ` [PATCH tip/core/rcu 04/15] rcu: Permit RCU_NONIDLE() to be used from interrupt context Paul E. McKenney
2012-08-30 18:56   ` [PATCH tip/core/rcu 05/15] rcu: Improve boost selection when moving tasks to root rcu_node Paul E. McKenney
2012-08-31 18:09     ` Josh Triplett
2012-08-30 18:56   ` [PATCH tip/core/rcu 06/15] rcu: Make offline-CPU checking allow for indefinite delays Paul E. McKenney
2012-08-31 18:12     ` Josh Triplett
2012-08-30 18:56   ` [PATCH tip/core/rcu 07/15] rcu: Fix obsolete rcu_initiate_boost() header comment Paul E. McKenney
2012-08-31 18:13     ` Josh Triplett
2012-08-30 18:56   ` [PATCH tip/core/rcu 08/15] rcu: Apply for_each_rcu_flavor() to increment_cpu_stall_ticks() Paul E. McKenney
2012-08-31 18:15     ` Josh Triplett
2012-09-04 22:44       ` Paul E. McKenney
2012-08-30 18:56   ` [PATCH tip/core/rcu 09/15] rcu: Avoid rcu_print_detail_task_stall_rnp() segfault Paul E. McKenney
2012-08-31 18:19     ` Josh Triplett
2012-09-04 22:46       ` Paul E. McKenney
2012-09-04 22:55         ` Josh Triplett
2012-08-30 18:56   ` [PATCH tip/core/rcu 10/15] rcu: Protect rcu_node accesses during CPU stall warnings Paul E. McKenney
2012-08-31 18:23     ` Josh Triplett
2012-09-04 22:51       ` Paul E. McKenney
2012-09-06 14:51     ` Peter Zijlstra
2012-09-06 21:01       ` Paul E. McKenney
2012-08-30 18:56   ` [PATCH tip/core/rcu 11/15] rcu: Avoid spurious RCU " Paul E. McKenney
2012-08-31 18:24     ` Josh Triplett
2012-09-06 14:56     ` Peter Zijlstra
2012-09-06 15:07       ` Steven Rostedt
2012-09-06 15:19         ` Peter Zijlstra
2012-09-06 21:03           ` Paul E. McKenney
2012-09-06 21:41             ` Steven Rostedt
2012-09-06 21:58               ` Paul E. McKenney
2012-09-06 22:05                 ` Steven Rostedt
2012-09-06 22:22                   ` Paul E. McKenney
2012-09-07  7:00                     ` Peter Zijlstra
2012-09-07 14:42                       ` Steven Rostedt
2012-08-30 18:56   ` [PATCH tip/core/rcu 12/15] rcu: Remove redundant memory barrier from __call_rcu() Paul E. McKenney
2012-08-31 18:30     ` Josh Triplett
2012-08-31 18:40       ` Josh Triplett
2012-08-30 18:56   ` [PATCH tip/core/rcu 13/15] rcu: Move TINY_PREEMPT_RCU away from raw_local_irq_save() Paul E. McKenney
2012-08-31 18:34     ` Josh Triplett
2012-09-04 23:03       ` Paul E. McKenney
2012-08-30 18:56   ` [PATCH tip/core/rcu 14/15] time: RCU permitted to stop idle entry via softirq Paul E. McKenney
2012-08-31 18:51     ` Josh Triplett
2012-09-06 15:12     ` Peter Zijlstra
2012-09-06 21:35       ` Paul E. McKenney
2012-09-06 21:57         ` Steven Rostedt
2012-09-06 22:11           ` Paul E. McKenney
2012-08-30 18:56   ` [PATCH tip/core/rcu 15/15] kmemleak: Replace list_for_each_continue_rcu with new interface Paul E. McKenney
2012-08-31 18:55     ` Josh Triplett
2012-09-04 23:41       ` Paul E. McKenney
2012-08-31 16:49   ` [PATCH tip/core/rcu 01/15] rcu: Add PROVE_RCU_DELAY to provoke difficult races Josh Triplett
2012-09-04 22:36     ` Paul E. McKenney
2012-09-06 14:38   ` Peter Zijlstra
2012-09-06 20:51     ` Paul E. McKenney
2012-09-07  6:54       ` Peter Zijlstra

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