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Re: [PATCH tip/core/rcu 0/20] Miscellaneous fixes for 4.11

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  Re: [PATCH tip/core/rcu 0/20] Miscellaneous fixes for 4.11 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-18 04:00 +0100
    [PATCH v2 tip/core/rcu 01/18] rcu: update: Make RCU_EXPEDITE_BOOT be the default "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-18 04:00 +0100
    [PATCH v2 tip/core/rcu 14/18] rcu: Enable RCU tracepoints by default to aid in debugging "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-18 04:00 +0100
    [PATCH v2 tip/core/rcu 08/18] rcu: Remove short-term CPU kicking "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-18 04:00 +0100
      Re: [PATCH v2 tip/core/rcu 08/18] rcu: Remove short-term CPU kicking Josh Triplett <josh@joshtriplett.org> - 2017-01-21 21:50 +0100
        Re: [PATCH v2 tip/core/rcu 08/18] rcu: Remove short-term CPU kicking "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-23 20:40 +0100
    [PATCH v2 tip/core/rcu 11/18] rcu: Don't wake rcuc/X kthreads on NOCB CPUs "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-18 04:10 +0100
    [PATCH v2 tip/core/rcu 15/18] rcu: Fix comment in rcu_organize_nocb_kthreads() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-18 04:30 +0100
    [PATCH v2 tip/core/rcu 06/18] rcu: Remove unused but set variable "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-18 04:40 +0100
    [PATCH v2 tip/core/rcu 13/18] rcu: Make rcu_cpu_starting() use its "cpu" argument "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-18 04:40 +0100
    [PATCH v2 tip/core/rcu 18/18] rcu: Add lockdep checks to synchronous expedited primitives "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-18 05:00 +0100
    [PATCH v2 tip/core/rcu 03/18] Fix: Disable sys_membarrier when nohz_full is enabled "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-18 05:40 +0100
    [PATCH v2 tip/core/rcu 12/18] rcu: Add comment headers to expedited-grace-period counter functions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-18 05:50 +0100
    [PATCH v2 tip/core/rcu 17/18] rcu: Eliminate unused expedited_normal counter "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-18 05:50 +0100
    [PATCH v2 tip/core/rcu 16/18] llist: Clarify comments about when locking is needed "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-18 06:20 +0100
    [PATCH v2 tip/core/rcu 02/18] lockdep: Make RCU suspicious-access splats use pr_err "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-18 06:40 +0100
      Re: [PATCH v2 tip/core/rcu 02/18] lockdep: Make RCU  suspicious-access splats use pr_err Josh Triplett <josh@joshtriplett.org> - 2017-01-21 21:50 +0100
        Re: [PATCH v2 tip/core/rcu 02/18] lockdep: Make RCU  suspicious-access splats use pr_err "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-23 20:40 +0100
          Re: [PATCH v2 tip/core/rcu 02/18] lockdep: Make RCU  suspicious-access splats use pr_err Josh Triplett <josh@joshtriplett.org> - 2017-01-23 23:40 +0100
            Re: [PATCH v2 tip/core/rcu 02/18] lockdep: Make RCU  suspicious-access splats use pr_err "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-24 01:20 +0100
    [PATCH v2 tip/core/rcu 05/18] rcu: Remove unneeded rcu_process_callbacks() declarations "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-18 07:10 +0100
    [PATCH v2 tip/core/rcu 07/18] rcu: Add long-term CPU kicking "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-18 07:10 +0100
      Re: [PATCH v2 tip/core/rcu 07/18] rcu: Add long-term CPU kicking Josh Triplett <josh@joshtriplett.org> - 2017-01-21 21:50 +0100
        Re: [PATCH v2 tip/core/rcu 07/18] rcu: Add long-term CPU kicking "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-23 20:40 +0100
          Re: [PATCH v2 tip/core/rcu 07/18] rcu: Add long-term CPU kicking Josh Triplett <josh@joshtriplett.org> - 2017-01-23 21:30 +0100
      Re: [PATCH v2 tip/core/rcu 07/18] rcu: Add long-term CPU kicking Josh Triplett <josh@joshtriplett.org> - 2017-01-21 21:50 +0100
    [PATCH v3 tip/core/rcu 0/18] Miscellaneous fixes for 4.11 "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-24 23:00 +0100
      [PATCH v3 tip/core/rcu 17/18] rcu: Eliminate unused expedited_normal counter "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-24 23:00 +0100
      [PATCH v3 tip/core/rcu 04/18] rcu: Only dump stalled-tasks stacks if there was a real stall "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-24 23:00 +0100
      [PATCH v3 tip/core/rcu 16/18] llist: Clarify comments about when locking is needed "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-24 23:00 +0100
      [PATCH v3 tip/core/rcu 06/18] rcu: Remove unused but set variable "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-24 23:00 +0100
      [PATCH v3 tip/core/rcu 05/18] rcu: Remove unneeded rcu_process_callbacks() declarations "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-24 23:00 +0100
      [PATCH v3 tip/core/rcu 02/18] lockdep: Make RCU suspicious-access splats use pr_err "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-24 23:00 +0100
      [PATCH v3 tip/core/rcu 12/18] rcu: Add comment headers to expedited-grace-period counter functions "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-24 23:00 +0100
      [PATCH v3 tip/core/rcu 14/18] rcu: Enable RCU tracepoints by default to aid in debugging "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-24 23:00 +0100
      [PATCH v3 tip/core/rcu 07/18] rcu: Add long-term CPU kicking "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-24 23:00 +0100
      [PATCH v3 tip/core/rcu 18/18] rcu: Add lockdep checks to synchronous expedited primitives "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-24 23:00 +0100
      [PATCH v3 tip/core/rcu 11/18] rcu: Don't wake rcuc/X kthreads on NOCB CPUs "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-24 23:00 +0100
      [PATCH v3 tip/core/rcu 13/18] rcu: Make rcu_cpu_starting() use its "cpu" argument "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-24 23:00 +0100
      [PATCH v3 tip/core/rcu 10/18] rcu: Re-enable TASKS_RCU for User Mode Linux "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-24 23:00 +0100
      [PATCH v3 tip/core/rcu 15/18] rcu: Fix comment in rcu_organize_nocb_kthreads() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2017-01-24 23:00 +0100

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#1561299 — [PATCH v2 tip/core/rcu 05/18] rcu: Remove unneeded rcu_process_callbacks() declarations

The declarations of __rcu_process_callbacks() and rcu_process_callbacks()
are not needed, as the definition of both of these functions appear before
any uses.  This commit therefore removes both declarations.

Reported-by: "Ahmed, Iftekhar" <ahmedi@oregonstate.edu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 kernel/rcu/tiny.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
index b23a4d076f3d..fa6a48d3917b 100644
--- a/kernel/rcu/tiny.c
+++ b/kernel/rcu/tiny.c
@@ -41,8 +41,6 @@
 
 /* Forward declarations for tiny_plugin.h. */
 struct rcu_ctrlblk;
-static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp);
-static void rcu_process_callbacks(struct softirq_action *unused);
 static void __call_rcu(struct rcu_head *head,
 		       rcu_callback_t func,
 		       struct rcu_ctrlblk *rcp);
-- 
2.5.2

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#1561304 — [PATCH v2 tip/core/rcu 07/18] rcu: Add long-term CPU kicking

Commit d2db185bfee8 ("rcu: Remove short-term CPU kicking") removed
frequent calls to resched_cpu(), which means that the only time
resched_cpu() is invoked is after an RCU CPU stall warning.  Although
this is good from an avoid-IPIs perspective, we should try to break
things loose -before- splatting.  This commit therefore starts invoking
resched_cpu() for each holdout at each force-quiescent-state interval
that is more than halfway through the stall-warning interval.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcu/tree.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 83bf054e194e..0e61b62e3f4a 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1225,6 +1225,12 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
 			 rdp->rsp->gp_start + 2 * jiffies_till_sched_qs) ||
 	    ULONG_CMP_GE(jiffies, rdp->rsp->gp_start + jiffies_till_sched_qs))
 		resched_cpu(rdp->cpu);  /* Force CPU into scheduler. */
+	/*
+	 * If more than halfway to RCU CPU stall-warning time, do
+	 * a resched_cpu() to try to loosen things up a bit.
+	 */
+	if (jiffies - rdp->rsp->gp_start > rcu_jiffies_till_stall_check() / 2)
+		resched_cpu(rdp->cpu);
 
 	return 0;
 }
-- 
2.5.2

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#1564241 — Re: [PATCH v2 tip/core/rcu 07/18] rcu: Add long-term CPU kicking

On Tue, Jan 17, 2017 at 06:53:46PM -0800, Paul E. McKenney wrote:
> Commit d2db185bfee8 ("rcu: Remove short-term CPU kicking") removed
> frequent calls to resched_cpu(), which means that the only time
> resched_cpu() is invoked is after an RCU CPU stall warning.  Although
> this is good from an avoid-IPIs perspective, we should try to break
> things loose -before- splatting.  This commit therefore starts invoking
> resched_cpu() for each holdout at each force-quiescent-state interval
> that is more than halfway through the stall-warning interval.

Just realized an issue with this commit message: you're referring to
what now appears as patch 8 in the past tense as something already done,
and with a commit ID that probably doesn't work anymore.  You need to
rephrase this to describe how it leads to a *subsequent* change rather
than fixing something already changed.

With the commit message fixed:
Reviewed-by: Josh Triplett <josh@joshtriplett.org>

> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>



> ---
>  kernel/rcu/tree.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 83bf054e194e..0e61b62e3f4a 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -1225,6 +1225,12 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
>  			 rdp->rsp->gp_start + 2 * jiffies_till_sched_qs) ||
>  	    ULONG_CMP_GE(jiffies, rdp->rsp->gp_start + jiffies_till_sched_qs))
>  		resched_cpu(rdp->cpu);  /* Force CPU into scheduler. */
> +	/*
> +	 * If more than halfway to RCU CPU stall-warning time, do
> +	 * a resched_cpu() to try to loosen things up a bit.
> +	 */
> +	if (jiffies - rdp->rsp->gp_start > rcu_jiffies_till_stall_check() / 2)
> +		resched_cpu(rdp->cpu);
>  
>  	return 0;
>  }
> -- 
> 2.5.2
> 

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#1565259 — Re: [PATCH v2 tip/core/rcu 07/18] rcu: Add long-term CPU kicking

On Sat, Jan 21, 2017 at 12:42:55PM -0800, Josh Triplett wrote:
> On Tue, Jan 17, 2017 at 06:53:46PM -0800, Paul E. McKenney wrote:
> > Commit d2db185bfee8 ("rcu: Remove short-term CPU kicking") removed
> > frequent calls to resched_cpu(), which means that the only time
> > resched_cpu() is invoked is after an RCU CPU stall warning.  Although
> > this is good from an avoid-IPIs perspective, we should try to break
> > things loose -before- splatting.  This commit therefore starts invoking
> > resched_cpu() for each holdout at each force-quiescent-state interval
> > that is more than halfway through the stall-warning interval.
> 
> Just realized an issue with this commit message: you're referring to
> what now appears as patch 8 in the past tense as something already done,
> and with a commit ID that probably doesn't work anymore.  You need to
> rephrase this to describe how it leads to a *subsequent* change rather
> than fixing something already changed.
> 
> With the commit message fixed:
> Reviewed-by: Josh Triplett <josh@joshtriplett.org>

Good point!  It now reads as follows:

------------------------------------------------------------------------
This commit prepares for the removal of short-term CPU kicking (in a
subsequent commit).  It does so by starting to invoke resched_cpu()
for each holdout at each force-quiescent-state interval that is more
than halfway through the stall-warning interval.
------------------------------------------------------------------------

Does that work?

							Thanx, Paul

> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> 
> 
> 
> > ---
> >  kernel/rcu/tree.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index 83bf054e194e..0e61b62e3f4a 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -1225,6 +1225,12 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
> >  			 rdp->rsp->gp_start + 2 * jiffies_till_sched_qs) ||
> >  	    ULONG_CMP_GE(jiffies, rdp->rsp->gp_start + jiffies_till_sched_qs))
> >  		resched_cpu(rdp->cpu);  /* Force CPU into scheduler. */
> > +	/*
> > +	 * If more than halfway to RCU CPU stall-warning time, do
> > +	 * a resched_cpu() to try to loosen things up a bit.
> > +	 */
> > +	if (jiffies - rdp->rsp->gp_start > rcu_jiffies_till_stall_check() / 2)
> > +		resched_cpu(rdp->cpu);
> >  
> >  	return 0;
> >  }
> > -- 
> > 2.5.2
> > 
> 

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#1565287 — Re: [PATCH v2 tip/core/rcu 07/18] rcu: Add long-term CPU kicking

On Mon, Jan 23, 2017 at 11:34:45AM -0800, Paul E. McKenney wrote:
> On Sat, Jan 21, 2017 at 12:42:55PM -0800, Josh Triplett wrote:
> > On Tue, Jan 17, 2017 at 06:53:46PM -0800, Paul E. McKenney wrote:
> > > Commit d2db185bfee8 ("rcu: Remove short-term CPU kicking") removed
> > > frequent calls to resched_cpu(), which means that the only time
> > > resched_cpu() is invoked is after an RCU CPU stall warning.  Although
> > > this is good from an avoid-IPIs perspective, we should try to break
> > > things loose -before- splatting.  This commit therefore starts invoking
> > > resched_cpu() for each holdout at each force-quiescent-state interval
> > > that is more than halfway through the stall-warning interval.
> > 
> > Just realized an issue with this commit message: you're referring to
> > what now appears as patch 8 in the past tense as something already done,
> > and with a commit ID that probably doesn't work anymore.  You need to
> > rephrase this to describe how it leads to a *subsequent* change rather
> > than fixing something already changed.
> > 
> > With the commit message fixed:
> > Reviewed-by: Josh Triplett <josh@joshtriplett.org>
> 
> Good point!  It now reads as follows:
> 
> ------------------------------------------------------------------------
> This commit prepares for the removal of short-term CPU kicking (in a
> subsequent commit).  It does so by starting to invoke resched_cpu()
> for each holdout at each force-quiescent-state interval that is more
> than halfway through the stall-warning interval.
> ------------------------------------------------------------------------
> 
> Does that work?

Looks good to me.

> 							Thanx, Paul
> 
> > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > 
> > 
> > 
> > > ---
> > >  kernel/rcu/tree.c | 6 ++++++
> > >  1 file changed, 6 insertions(+)
> > > 
> > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > > index 83bf054e194e..0e61b62e3f4a 100644
> > > --- a/kernel/rcu/tree.c
> > > +++ b/kernel/rcu/tree.c
> > > @@ -1225,6 +1225,12 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
> > >  			 rdp->rsp->gp_start + 2 * jiffies_till_sched_qs) ||
> > >  	    ULONG_CMP_GE(jiffies, rdp->rsp->gp_start + jiffies_till_sched_qs))
> > >  		resched_cpu(rdp->cpu);  /* Force CPU into scheduler. */
> > > +	/*
> > > +	 * If more than halfway to RCU CPU stall-warning time, do
> > > +	 * a resched_cpu() to try to loosen things up a bit.
> > > +	 */
> > > +	if (jiffies - rdp->rsp->gp_start > rcu_jiffies_till_stall_check() / 2)
> > > +		resched_cpu(rdp->cpu);
> > >  
> > >  	return 0;
> > >  }
> > > -- 
> > > 2.5.2
> > > 
> > 
> 

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#1564248 — Re: [PATCH v2 tip/core/rcu 07/18] rcu: Add long-term CPU kicking

On Tue, Jan 17, 2017 at 06:53:46PM -0800, Paul E. McKenney wrote:
> Commit d2db185bfee8 ("rcu: Remove short-term CPU kicking") removed
> frequent calls to resched_cpu(), which means that the only time
> resched_cpu() is invoked is after an RCU CPU stall warning.  Although
> this is good from an avoid-IPIs perspective, we should try to break
> things loose -before- splatting.  This commit therefore starts invoking
> resched_cpu() for each holdout at each force-quiescent-state interval
> that is more than halfway through the stall-warning interval.
> 
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

Reviewed-by: Josh Triplett <josh@joshtriplett.org>

> ---
>  kernel/rcu/tree.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 83bf054e194e..0e61b62e3f4a 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -1225,6 +1225,12 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
>  			 rdp->rsp->gp_start + 2 * jiffies_till_sched_qs) ||
>  	    ULONG_CMP_GE(jiffies, rdp->rsp->gp_start + jiffies_till_sched_qs))
>  		resched_cpu(rdp->cpu);  /* Force CPU into scheduler. */
> +	/*
> +	 * If more than halfway to RCU CPU stall-warning time, do
> +	 * a resched_cpu() to try to loosen things up a bit.
> +	 */
> +	if (jiffies - rdp->rsp->gp_start > rcu_jiffies_till_stall_check() / 2)
> +		resched_cpu(rdp->cpu);
>  
>  	return 0;
>  }
> -- 
> 2.5.2
> 

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#1566174 — [PATCH v3 tip/core/rcu 0/18] Miscellaneous fixes for 4.11

Hello!

This series provides v3 of miscellaneous fixes:

1.	Make RCU_EXPEDITE_BOOT be the default in order to speed up
	boot, courtesy of Sebastian Andrzej Siewior.

2.	Make RCU suspicious-access lockdep splats use pr_err().

3.	Disable sys_membarrier when nohz_full is enabled, courtesy
	of Mathieu Desnoyers.

4.	Only dump stalled-tasks stacks if there was a real stall, courtesy
	of Byungchul Park.

5.	Remove unneeded rcu_process_callbacks() declarations.

6.	Remove unused but set "mask" variable, courtesy of Tobias Klauser.

7.	Add long-term CPU kicking.

8.	Remove short-term CPU kicking.

9.	Once again use NMI-based stack traces in stall warnings.

10.	Re-enable TASKS_RCU for User Mode Linux.

11.	Don't wake rcuc/X kthreads on NOCB CPUs.

12.	Add comment headers to expedited-grace-period counter functions.

13.	Make rcu_cpu_starting() use its "cpu" argument.

14.	Enable RCU tracepoints by default to aid in debugging, courtesy
	of Matt Fleming.

15.	Fix comment in rcu_organize_nocb_kthreads(), which no longer
	spawns kthreads.

16.	Clarify comments about when llist locking is needed, courtesy
	of Joel Fernandes.

17.	Eliminate unused expedited_normal counter.

18.	Add lockdep checks to synchronous expedited primitives.

Changes since v2:

o	Fixed lockdep message as noted by Josh Triplett.

Changes since v1:

o	Reverse the order of patches 7 and 8.

o	Defer the patch adding tests for trivial grace periods.

o	Defer the patch making cond_resched() provide RCU quiescent
	states.

o	Apply other feedback from Josh Triplett, Peter Zijlstra, and
	Michal Hocko.

							Thanx, Paul

------------------------------------------------------------------------

 Documentation/RCU/trace.txt |    5 +----
 include/linux/llist.h       |   37 +++++++++++++++++++++----------------
 init/Kconfig                |   14 --------------
 kernel/locking/lockdep.c    |   12 ++++++------
 kernel/membarrier.c         |    4 ++++
 kernel/rcu/tiny.c           |    2 --
 kernel/rcu/tree.c           |   35 ++++++++++++++++++-----------------
 kernel/rcu/tree.h           |    1 -
 kernel/rcu/tree_exp.h       |   28 +++++++++++++++++++++++++++-
 kernel/rcu/tree_plugin.h    |    5 +++--
 kernel/rcu/tree_trace.c     |    3 +--
 kernel/rcu/update.c         |    6 ++----
 lib/Kconfig.debug           |    1 +
 13 files changed, 84 insertions(+), 69 deletions(-)

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#1566175 — [PATCH v3 tip/core/rcu 17/18] rcu: Eliminate unused expedited_normal counter

Expedited grace periods no longer fall back to normal grace periods
in response to lock contention, given that expedited grace periods
now use the rcu_node tree so as to avoid contention.  This commit
therfore removes the expedited_normal counter.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 Documentation/RCU/trace.txt | 5 +----
 kernel/rcu/tree.h           | 1 -
 kernel/rcu/tree_trace.c     | 3 +--
 3 files changed, 2 insertions(+), 7 deletions(-)

diff --git a/Documentation/RCU/trace.txt b/Documentation/RCU/trace.txt
index 00a3a38b375a..6549012033f9 100644
--- a/Documentation/RCU/trace.txt
+++ b/Documentation/RCU/trace.txt
@@ -237,7 +237,7 @@ o	"ktl" is the low-order 16 bits (in hexadecimal) of the count of
 
 The output of "cat rcu/rcu_preempt/rcuexp" looks as follows:
 
-s=21872 wd1=0 wd2=0 wd3=5 n=0 enq=0 sc=21872
+s=21872 wd1=0 wd2=0 wd3=5 enq=0 sc=21872
 
 These fields are as follows:
 
@@ -249,9 +249,6 @@ o	"wd1", "wd2", and "wd3" are the number of times that an attempt
 	completed an expedited grace period that satisfies the attempted
 	request.  "Our work is done."
 
-o	"n" is number of times that a concurrent CPU-hotplug operation
-	forced a fallback to a normal grace period.
-
 o	"enq" is the number of quiescent states still outstanding.
 
 o	"sc" is the number of times that the attempt to start a
diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
index fe98dd24adf8..8f750dffb0dd 100644
--- a/kernel/rcu/tree.h
+++ b/kernel/rcu/tree.h
@@ -521,7 +521,6 @@ struct rcu_state {
 	struct mutex exp_mutex;			/* Serialize expedited GP. */
 	struct mutex exp_wake_mutex;		/* Serialize wakeup. */
 	unsigned long expedited_sequence;	/* Take a ticket. */
-	atomic_long_t expedited_normal;		/* # fallbacks to normal. */
 	atomic_t expedited_need_qs;		/* # CPUs left to check in. */
 	struct swait_queue_head expedited_wq;	/* Wait for check-ins. */
 	int ncpus_snap;				/* # CPUs seen last time. */
diff --git a/kernel/rcu/tree_trace.c b/kernel/rcu/tree_trace.c
index b1f28972872c..2e932cd1da31 100644
--- a/kernel/rcu/tree_trace.c
+++ b/kernel/rcu/tree_trace.c
@@ -194,9 +194,8 @@ static int show_rcuexp(struct seq_file *m, void *v)
 		s2 += atomic_long_read(&rdp->exp_workdone2);
 		s3 += atomic_long_read(&rdp->exp_workdone3);
 	}
-	seq_printf(m, "s=%lu wd0=%lu wd1=%lu wd2=%lu wd3=%lu n=%lu enq=%d sc=%lu\n",
+	seq_printf(m, "s=%lu wd0=%lu wd1=%lu wd2=%lu wd3=%lu enq=%d sc=%lu\n",
 		   rsp->expedited_sequence, s0, s1, s2, s3,
-		   atomic_long_read(&rsp->expedited_normal),
 		   atomic_read(&rsp->expedited_need_qs),
 		   rsp->expedited_sequence / 2);
 	return 0;
-- 
2.5.2

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#1566176 — [PATCH v3 tip/core/rcu 04/18] rcu: Only dump stalled-tasks stacks if there was a real stall

From: Byungchul Park <byungchul.park@lge.com>

The print_other_cpu_stall() function currently unconditionally invokes
rcu_print_detail_task_stall().  This is OK because if there was a stall
sufficient to cause print_other_cpu_stall() to be invoked, that stall
is very likely to persist through the entire print_other_cpu_stall()
execution.  However, if the stall did not persist, the variable ndetected
will be zero, and that variable is already tested in an "if" statement.
Therefore, this commit moves the call to rcu_print_detail_task_stall()
under that pre-existing "if" to improve readability, with a very rare
reduction in overhead.

Signed-off-by: Byungchul Park <byungchul.park@lge.com>
[ paulmck: Reworked commit log. ]
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 kernel/rcu/tree.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index cb4e2056ccf3..6232d2f9a84e 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1379,6 +1379,9 @@ static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
 	       (long)rsp->gpnum, (long)rsp->completed, totqlen);
 	if (ndetected) {
 		rcu_dump_cpu_stacks(rsp);
+
+		/* Complain about tasks blocking the grace period. */
+		rcu_print_detail_task_stall(rsp);
 	} else {
 		if (READ_ONCE(rsp->gpnum) != gpnum ||
 		    READ_ONCE(rsp->completed) == gpnum) {
@@ -1395,9 +1398,6 @@ static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gpnum)
 		}
 	}
 
-	/* Complain about tasks blocking the grace period. */
-	rcu_print_detail_task_stall(rsp);
-
 	rcu_check_gp_kthread_starvation(rsp);
 
 	panic_on_rcu_stall();
-- 
2.5.2

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#1566177 — [PATCH v3 tip/core/rcu 16/18] llist: Clarify comments about when locking is needed

From: Joel Fernandes <joelaf@google.com>

llist.h comments are confusing about when locking is needed versus when it
isn't. Clarify these comments by being more descriptive about why locking is
needed for llist_del_first.

Cc: Ingo Molnar <mingo@kernel.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Paul McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: Huang Ying <ying.huang@intel.com>
Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Joel Fernandes <joelaf@google.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 include/linux/llist.h | 37 +++++++++++++++++++++----------------
 1 file changed, 21 insertions(+), 16 deletions(-)

diff --git a/include/linux/llist.h b/include/linux/llist.h
index fd4ca0b4fe0f..171baa90f6f6 100644
--- a/include/linux/llist.h
+++ b/include/linux/llist.h
@@ -3,28 +3,33 @@
 /*
  * Lock-less NULL terminated single linked list
  *
- * If there are multiple producers and multiple consumers, llist_add
- * can be used in producers and llist_del_all can be used in
- * consumers.  They can work simultaneously without lock.  But
- * llist_del_first can not be used here.  Because llist_del_first
- * depends on list->first->next does not changed if list->first is not
- * changed during its operation, but llist_del_first, llist_add,
- * llist_add (or llist_del_all, llist_add, llist_add) sequence in
- * another consumer may violate that.
- *
- * If there are multiple producers and one consumer, llist_add can be
- * used in producers and llist_del_all or llist_del_first can be used
- * in the consumer.
- *
- * This can be summarized as follow:
+ * Cases where locking is not needed:
+ * If there are multiple producers and multiple consumers, llist_add can be
+ * used in producers and llist_del_all can be used in consumers simultaneously
+ * without locking. Also a single consumer can use llist_del_first while
+ * multiple producers simultaneously use llist_add, without any locking.
+ *
+ * Cases where locking is needed:
+ * If we have multiple consumers with llist_del_first used in one consumer, and
+ * llist_del_first or llist_del_all used in other consumers, then a lock is
+ * needed.  This is because llist_del_first depends on list->first->next not
+ * changing, but without lock protection, there's no way to be sure about that
+ * if a preemption happens in the middle of the delete operation and on being
+ * preempted back, the list->first is the same as before causing the cmpxchg in
+ * llist_del_first to succeed. For example, while a llist_del_first operation
+ * is in progress in one consumer, then a llist_del_first, llist_add,
+ * llist_add (or llist_del_all, llist_add, llist_add) sequence in another
+ * consumer may cause violations.
+ *
+ * This can be summarized as follows:
  *
  *           |   add    | del_first |  del_all
  * add       |    -     |     -     |     -
  * del_first |          |     L     |     L
  * del_all   |          |           |     -
  *
- * Where "-" stands for no lock is needed, while "L" stands for lock
- * is needed.
+ * Where, a particular row's operation can happen concurrently with a column's
+ * operation, with "-" being no lock needed, while "L" being lock is needed.
  *
  * The list entries deleted via llist_del_all can be traversed with
  * traversing function such as llist_for_each etc.  But the list
-- 
2.5.2

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#1566178 — [PATCH v3 tip/core/rcu 06/18] rcu: Remove unused but set variable

From: Tobias Klauser <tklauser@distanz.ch>

Since commit 7ec99de36f40 ("rcu: Provide exact CPU-online tracking for
RCU"), the variable mask in rcu_init_percpu_data is set but no longer
used. Remove it to fix the following warning when building with 'W=1':

  kernel/rcu/tree.c: In function ‘rcu_init_percpu_data’:
  kernel/rcu/tree.c:3765:16: warning: variable ‘mask’ set but not used [-Wunused-but-set-variable]

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 kernel/rcu/tree.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 6232d2f9a84e..83bf054e194e 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3765,7 +3765,6 @@ static void
 rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
 {
 	unsigned long flags;
-	unsigned long mask;
 	struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
 	struct rcu_node *rnp = rcu_get_root(rsp);
 
@@ -3788,7 +3787,6 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
 	 * of the next grace period.
 	 */
 	rnp = rdp->mynode;
-	mask = rdp->grpmask;
 	raw_spin_lock_rcu_node(rnp);		/* irqs already disabled. */
 	if (!rdp->beenonline)
 		WRITE_ONCE(rsp->ncpus, READ_ONCE(rsp->ncpus) + 1);
-- 
2.5.2

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#1566179 — [PATCH v3 tip/core/rcu 05/18] rcu: Remove unneeded rcu_process_callbacks() declarations

The declarations of __rcu_process_callbacks() and rcu_process_callbacks()
are not needed, as the definition of both of these functions appear before
any uses.  This commit therefore removes both declarations.

Reported-by: "Ahmed, Iftekhar" <ahmedi@oregonstate.edu>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 kernel/rcu/tiny.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c
index b23a4d076f3d..fa6a48d3917b 100644
--- a/kernel/rcu/tiny.c
+++ b/kernel/rcu/tiny.c
@@ -41,8 +41,6 @@
 
 /* Forward declarations for tiny_plugin.h. */
 struct rcu_ctrlblk;
-static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp);
-static void rcu_process_callbacks(struct softirq_action *unused);
 static void __call_rcu(struct rcu_head *head,
 		       rcu_callback_t func,
 		       struct rcu_ctrlblk *rcp);
-- 
2.5.2

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#1566180 — [PATCH v3 tip/core/rcu 02/18] lockdep: Make RCU suspicious-access splats use pr_err

This commit switches RCU suspicious-access splats use pr_err()
instead of the current INFO printk()s.  This change makes it easier
to automatically classify splats.

Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/locking/lockdep.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/kernel/locking/lockdep.c b/kernel/locking/lockdep.c
index 7c38f8f3d97b..d9a698e8458f 100644
--- a/kernel/locking/lockdep.c
+++ b/kernel/locking/lockdep.c
@@ -4412,13 +4412,13 @@ void lockdep_rcu_suspicious(const char *file, const int line, const char *s)
 #endif /* #ifdef CONFIG_PROVE_RCU_REPEATEDLY */
 	/* Note: the following can be executed concurrently, so be careful. */
 	printk("\n");
-	printk("===============================\n");
-	printk("[ INFO: suspicious RCU usage. ]\n");
+	pr_err("===============================\n");
+	pr_err("[ ERR: suspicious RCU usage.  ]\n");
 	print_kernel_ident();
-	printk("-------------------------------\n");
-	printk("%s:%d %s!\n", file, line, s);
-	printk("\nother info that might help us debug this:\n\n");
-	printk("\n%srcu_scheduler_active = %d, debug_locks = %d\n",
+	pr_err("-------------------------------\n");
+	pr_err("%s:%d %s!\n", file, line, s);
+	pr_err("\nother info that might help us debug this:\n\n");
+	pr_err("\n%srcu_scheduler_active = %d, debug_locks = %d\n",
 	       !rcu_lockdep_current_cpu_online()
 			? "RCU used illegally from offline CPU!\n"
 			: !rcu_is_watching()
-- 
2.5.2

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#1566181 — [PATCH v3 tip/core/rcu 12/18] rcu: Add comment headers to expedited-grace-period counter functions

These functions (rcu_exp_gp_seq_start(), rcu_exp_gp_seq_end(),
rcu_exp_gp_seq_snap(), and rcu_exp_gp_seq_done() seemed too obvious
to comment when written, but not so much when being documented.
This commit therefore adds header comments to each of them.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 kernel/rcu/tree_exp.h | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index e59e1849b89a..303df97bbfc5 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -20,16 +20,26 @@
  * Authors: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
  */
 
-/* Wrapper functions for expedited grace periods.  */
+/*
+ * Record the start of an expedited grace period.
+ */
 static void rcu_exp_gp_seq_start(struct rcu_state *rsp)
 {
 	rcu_seq_start(&rsp->expedited_sequence);
 }
+
+/*
+ * Record the end of an expedited grace period.
+ */
 static void rcu_exp_gp_seq_end(struct rcu_state *rsp)
 {
 	rcu_seq_end(&rsp->expedited_sequence);
 	smp_mb(); /* Ensure that consecutive grace periods serialize. */
 }
+
+/*
+ * Take a snapshot of the expedited-grace-period counter.
+ */
 static unsigned long rcu_exp_gp_seq_snap(struct rcu_state *rsp)
 {
 	unsigned long s;
@@ -39,6 +49,12 @@ static unsigned long rcu_exp_gp_seq_snap(struct rcu_state *rsp)
 	trace_rcu_exp_grace_period(rsp->name, s, TPS("snap"));
 	return s;
 }
+
+/*
+ * Given a counter snapshot from rcu_exp_gp_seq_snap(), return true
+ * if a full expedited grace period has elapsed since that snapshot
+ * was taken.
+ */
 static bool rcu_exp_gp_seq_done(struct rcu_state *rsp, unsigned long s)
 {
 	return rcu_seq_done(&rsp->expedited_sequence, s);
-- 
2.5.2

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#1566182 — [PATCH v3 tip/core/rcu 14/18] rcu: Enable RCU tracepoints by default to aid in debugging

From: Matt Fleming <matt@codeblueprint.co.uk>

While debugging a performance issue I needed to understand why
RCU sofitrqs were firing so frequently.

Unfortunately, the RCU callback tracepoints are hidden behind
CONFIG_RCU_TRACE which defaults to off in the upstream kernel and is
likely to also be disabled in enterprise distribution configs.

Enable it by default for CONFIG_TREE_RCU. However, we must keep it
disabled for tiny RCU, because it would otherwise pull in a large
amount of code that would make tiny RCU less than tiny.

I ran some file system metadata intensive workloads (git checkout,
FS-Mark) on a variety of machines with this patch and saw no
detectable change in performance.

Cc: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 lib/Kconfig.debug | 1 +
 1 file changed, 1 insertion(+)

diff --git a/lib/Kconfig.debug b/lib/Kconfig.debug
index b06848a104e6..5655bd95919a 100644
--- a/lib/Kconfig.debug
+++ b/lib/Kconfig.debug
@@ -1450,6 +1450,7 @@ config RCU_CPU_STALL_TIMEOUT
 config RCU_TRACE
 	bool "Enable tracing for RCU"
 	depends on DEBUG_KERNEL
+	default y if TREE_RCU
 	select TRACE_CLOCK
 	help
 	  This option provides tracing in RCU which presents stats
-- 
2.5.2

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#1566183 — [PATCH v3 tip/core/rcu 07/18] rcu: Add long-term CPU kicking

This commit prepares for the removal of short-term CPU kicking (in a
subsequent commit).  It does so by starting to invoke resched_cpu()
for each holdout at each force-quiescent-state interval that is more
than halfway through the stall-warning interval.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 kernel/rcu/tree.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 83bf054e194e..0e61b62e3f4a 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -1225,6 +1225,12 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
 			 rdp->rsp->gp_start + 2 * jiffies_till_sched_qs) ||
 	    ULONG_CMP_GE(jiffies, rdp->rsp->gp_start + jiffies_till_sched_qs))
 		resched_cpu(rdp->cpu);  /* Force CPU into scheduler. */
+	/*
+	 * If more than halfway to RCU CPU stall-warning time, do
+	 * a resched_cpu() to try to loosen things up a bit.
+	 */
+	if (jiffies - rdp->rsp->gp_start > rcu_jiffies_till_stall_check() / 2)
+		resched_cpu(rdp->cpu);
 
 	return 0;
 }
-- 
2.5.2

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#1566184 — [PATCH v3 tip/core/rcu 18/18] rcu: Add lockdep checks to synchronous expedited primitives

The non-expedited synchronize_*rcu() primitives have lockdep checks, but
their expedited counterparts lack these checks.  This commit therefore
adds these checks to the expedited synchronize_*rcu() primitives.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 kernel/rcu/tree_exp.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
index 303df97bbfc5..f3e214898e3a 100644
--- a/kernel/rcu/tree_exp.h
+++ b/kernel/rcu/tree_exp.h
@@ -639,6 +639,11 @@ void synchronize_sched_expedited(void)
 {
 	struct rcu_state *rsp = &rcu_sched_state;
 
+	RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
+			 lock_is_held(&rcu_lock_map) ||
+			 lock_is_held(&rcu_sched_lock_map),
+			 "Illegal synchronize_sched_expedited() in RCU read-side critical section");
+
 	/* If only one CPU, this is automatically a grace period. */
 	if (rcu_blocking_is_gp())
 		return;
@@ -708,6 +713,11 @@ void synchronize_rcu_expedited(void)
 {
 	struct rcu_state *rsp = rcu_state_p;
 
+	RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
+			 lock_is_held(&rcu_lock_map) ||
+			 lock_is_held(&rcu_sched_lock_map),
+			 "Illegal synchronize_rcu_expedited() in RCU read-side critical section");
+
 	if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
 		return;
 	_synchronize_rcu_expedited(rsp, sync_rcu_exp_handler);
-- 
2.5.2

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#1566185 — [PATCH v3 tip/core/rcu 11/18] rcu: Don't wake rcuc/X kthreads on NOCB CPUs

Chris Friesen notice that rcuc/X kthreads were consuming CPU even on
NOCB CPUs.  This makes no sense because the only purpose or these
kthreads is to invoke normal (non-offloaded) callbacks, of which there
will never be any on NOCB CPUs.  This problem was due to a bug in
cpu_has_callbacks_ready_to_invoke(), which should have been checking
->nxttail[RCU_NEXT_TAIL] for NULL, but which was instead (incorrectly)
checking ->nxttail[RCU_DONE_TAIL].  Because ->nxttail[RCU_DONE_TAIL] is
never NULL, the only effect is to cause the rcuc/X kthread to execute
when it should not do so.

This commit therefore checks ->nxttail[RCU_NEXT_TAIL], which is NULL
for NOCB CPUs.

Reported-by: Chris Friesen <chris.friesen@windriver.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 kernel/rcu/tree.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index d7b63b88434b..be2301238a23 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -611,7 +611,7 @@ static int
 cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
 {
 	return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL] &&
-	       rdp->nxttail[RCU_DONE_TAIL] != NULL;
+	       rdp->nxttail[RCU_NEXT_TAIL] != NULL;
 }
 
 /*
-- 
2.5.2

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#1566187 — [PATCH v3 tip/core/rcu 13/18] rcu: Make rcu_cpu_starting() use its "cpu" argument

The rcu_cpu_starting() function uses this_cpu_ptr() to locate the
incoming CPU's rcu_data structure.  This works for the boot CPU and for
all CPUs onlined after rcu_init() executes (during very early boot).
Currently, this is the full set of CPUs, so all is well.  But if
anyone ever parallelizes boot before rcu_init() time, it will fail.
This commit therefore substitutes the rcu_cpu_starting() function's
this_cpu_pointer() for per_cpu_ptr(), future-proofing the code and
(arguably) improving readability.

This commit inadvertently fixes a latent bug: If there ever had been
more than just the boot CPU online at rcu_init() time, the old code
would not initialize the non-boot CPUs, but rather would repeatedly
initialize the boot CPU.

Reported-by: Boqun Feng <boqun.feng@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 kernel/rcu/tree.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index be2301238a23..a4b4762442bb 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3873,7 +3873,7 @@ void rcu_cpu_starting(unsigned int cpu)
 	struct rcu_state *rsp;
 
 	for_each_rcu_flavor(rsp) {
-		rdp = this_cpu_ptr(rsp->rda);
+		rdp = per_cpu_ptr(rsp->rda, cpu);
 		rnp = rdp->mynode;
 		mask = rdp->grpmask;
 		raw_spin_lock_irqsave_rcu_node(rnp, flags);
-- 
2.5.2

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#1566188 — [PATCH v3 tip/core/rcu 10/18] rcu: Re-enable TASKS_RCU for User Mode Linux

Now that User Mode Linux supports arch_irqs_disabled_flags(), this
commit re-enables TASKS_RCU for User Mode Linux.

Reported-by: Richard Weinberger <richard@nod.at>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
---
 init/Kconfig | 1 -
 1 file changed, 1 deletion(-)

diff --git a/init/Kconfig b/init/Kconfig
index 96e6d56acd50..d0caacb4bc14 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -529,7 +529,6 @@ config SRCU
 config TASKS_RCU
 	bool
 	default n
-	depends on !UML
 	select SRCU
 	help
 	  This option enables a task-based RCU implementation that uses
-- 
2.5.2

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