[PATCH tip/core/rcu 0/3] rcu: improve diagnostics and documentation of source files

[PATCH tip/core/rcu 0/3] rcu: improve diagnostics and documentation of source files

[Paul E. McKenney]

Hello!

This patch set corrects the file specifiers for the RCU sources in the
MAINTAINERS file and also makes a couple of minor improvements to RCU's
diagnostics.

							Thanx, Paul


 MAINTAINERS             |   14 +++++++-------
 kernel/rcutree.c        |   10 ++++++++--
 kernel/rcutree_plugin.h |    4 +++-
 3 files changed, 18 insertions(+), 10 deletions(-)

[PATCH tip/core/rcu 1/3] rcu: make MAINTAINERS file match new RCU reality

[Paul E. McKenney]

Both rcutorture and RCU are supported.  Also, update the files
to match the new layout.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 MAINTAINERS |   13 +++++++------
 1 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/MAINTAINERS b/MAINTAINERS
index e1da925..21c9d3b 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4335,7 +4335,7 @@ F:	drivers/net/wireless/ray*
 RCUTORTURE MODULE
 M:	Josh Triplett <josh@freedesktop.org>
 M:	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
-S:	Maintained
+S:	Supported
 F:	Documentation/RCU/torture.txt
 F:	kernel/rcutorture.c
 
@@ -4360,11 +4360,12 @@ M:	Dipankar Sarma <dipankar@in.ibm.com>
 M:	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
 W:	http://www.rdrop.com/users/paulmck/rclock/
 S:	Supported
-F:	Documentation/RCU/rcu.txt
-F:	Documentation/RCU/rcuref.txt
-F:	include/linux/rcupdate.h
-F:	include/linux/srcu.h
-F:	kernel/rcupdate.c
+F:	Documentation/RCU/
+F:	include/linux/rcu*
+F:	include/linux/srcu*
+F:	kernel/rcu*
+F:	kernel/srcu*
+X:	kernel/rcutorture.c
 
 REAL TIME CLOCK DRIVER
 M:	Paul Gortmaker <p_gortmaker@yahoo.com>
-- 
1.5.2.5

[PATCH tip/core/rcu 2/3] rcu: add debug check for too many rcu_read_unlock()

[Paul E. McKenney]

From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

TREE_PREEMPT_RCU maintains an rcu_read_lock_nesting counter in the
task structure, which happens to be a signed int.  So this patch adds a
check for this counter being negative at the end of __rcu_read_unlock().
This check is under CONFIG_PROVE_LOCKING, so can be thought of as being
part of lockdep.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcutree_plugin.h |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index f11ebd4..e77cdf3 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -304,6 +304,9 @@ void __rcu_read_unlock(void)
 	if (--ACCESS_ONCE(t->rcu_read_lock_nesting) == 0 &&
 	    unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
 		rcu_read_unlock_special(t);
+#ifdef CONFIG_PROVE_LOCKING
+	WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0);
+#endif /* #ifdef CONFIG_PROVE_LOCKING */
 }
 EXPORT_SYMBOL_GPL(__rcu_read_unlock);
 
-- 
1.5.2.5

[PATCH tip/core/rcu 3/3] rcu: give different levels of the rcu_node hierarchy distinct lockdep names

[Paul E. McKenney]

From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

Previously, each level of the rcu_node hierarchy had the same rather
unimaginative name: "&rcu_node_class[i]".  This makes lockdep diagnostics
involving these lockdep classes less helpful than would be nice.
This patch fixes this by giving each level of the rcu_node hierarchy
a distinct name: "rcu_node_level_0", "rcu_node_level_1", and so on.
This version of the patch includes improved diagnostics suggested by
Josh Triplett and Peter Zijlstra.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
---
 kernel/rcutree.c |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 0a4c328..3b13d64 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1811,11 +1811,17 @@ static void __init rcu_init_levelspread(struct rcu_state *rsp)
  */
 static void __init rcu_init_one(struct rcu_state *rsp)
 {
+	static char *buf[] = { "rcu_node_level_0",
+			       "rcu_node_level_1",
+			       "rcu_node_level_2",
+			       "rcu_node_level_3" };  /* Match MAX_RCU_LVLS */
 	int cpustride = 1;
 	int i;
 	int j;
 	struct rcu_node *rnp;
 
+	BUILD_BUG_ON(MAX_RCU_LVLS > ARRAY_SIZE(buf));  /* Fix buf[] init! */
+
 	/* Initialize the level-tracking arrays. */
 
 	for (i = 1; i < NUM_RCU_LVLS; i++)
@@ -1829,7 +1835,8 @@ static void __init rcu_init_one(struct rcu_state *rsp)
 		rnp = rsp->level[i];
 		for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) {
 			spin_lock_init(&rnp->lock);
-			lockdep_set_class(&rnp->lock, &rcu_node_class[i]);
+			lockdep_set_class_and_name(&rnp->lock,
+						   &rcu_node_class[i], buf[i]);
 			rnp->gpnum = 0;
 			rnp->qsmask = 0;
 			rnp->qsmaskinit = 0;
-- 
1.5.2.5

Re: [PATCH tip/core/rcu 2/3] rcu: add debug check for too many rcu_read_unlock()

[Josh Triplett]

On Mon, Jan 04, 2010 at 04:04:01PM -0800, Paul E. McKenney wrote:
> From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> 
> TREE_PREEMPT_RCU maintains an rcu_read_lock_nesting counter in the
> task structure, which happens to be a signed int.  So this patch adds a
> check for this counter being negative at the end of __rcu_read_unlock().
> This check is under CONFIG_PROVE_LOCKING, so can be thought of as being
> part of lockdep.
> 
> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> ---
>  kernel/rcutree_plugin.h |    3 +++
>  1 files changed, 3 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
> index f11ebd4..e77cdf3 100644
> --- a/kernel/rcutree_plugin.h
> +++ b/kernel/rcutree_plugin.h
> @@ -304,6 +304,9 @@ void __rcu_read_unlock(void)
>  	if (--ACCESS_ONCE(t->rcu_read_lock_nesting) == 0 &&
>  	    unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
>  		rcu_read_unlock_special(t);
> +#ifdef CONFIG_PROVE_LOCKING
> +	WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0);
> +#endif /* #ifdef CONFIG_PROVE_LOCKING */
>  }
>  EXPORT_SYMBOL_GPL(__rcu_read_unlock);

Given that you *already* need to access t->rcu_read_lock_nesting here,
why not just do the test all the time?  Ideally you could access
t->rcu_read_lock_nesting once, decrement it, and test for both 0 and
negative.

- Josh Triplett

Re: [PATCH tip/core/rcu 2/3] rcu: add debug check for too many rcu_read_unlock()

[Paul E. McKenney]

On Mon, Jan 04, 2010 at 06:03:08PM -0800, Josh Triplett wrote:
> On Mon, Jan 04, 2010 at 04:04:01PM -0800, Paul E. McKenney wrote:
> > From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > 
> > TREE_PREEMPT_RCU maintains an rcu_read_lock_nesting counter in the
> > task structure, which happens to be a signed int.  So this patch adds a
> > check for this counter being negative at the end of __rcu_read_unlock().
> > This check is under CONFIG_PROVE_LOCKING, so can be thought of as being
> > part of lockdep.
> > 
> > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > ---
> >  kernel/rcutree_plugin.h |    3 +++
> >  1 files changed, 3 insertions(+), 0 deletions(-)
> > 
> > diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
> > index f11ebd4..e77cdf3 100644
> > --- a/kernel/rcutree_plugin.h
> > +++ b/kernel/rcutree_plugin.h
> > @@ -304,6 +304,9 @@ void __rcu_read_unlock(void)
> >  	if (--ACCESS_ONCE(t->rcu_read_lock_nesting) == 0 &&
> >  	    unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
> >  		rcu_read_unlock_special(t);
> > +#ifdef CONFIG_PROVE_LOCKING
> > +	WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0);
> > +#endif /* #ifdef CONFIG_PROVE_LOCKING */
> >  }
> >  EXPORT_SYMBOL_GPL(__rcu_read_unlock);
> 
> Given that you *already* need to access t->rcu_read_lock_nesting here,
> why not just do the test all the time?  Ideally you could access
> t->rcu_read_lock_nesting once, decrement it, and test for both 0 and
> negative.

Because I was paranoid about the extra branch.  Perhaps needlessly
paranoid, but this is rcu_read_unlock() we are talking about here.  ;-)

You seem to be suggesting making the first test be "<=", then
sorting things out later, but given that both the equals-zero and the
greater-than-zero cases are quite common, I couldn't figure out how to
avoid the extra test and branch in the common case.  Hence the #ifdef.

							Thanx, Paul

Re: [PATCH tip/core/rcu 2/3] rcu: add debug check for too many rcu_read_unlock()

[Josh Triplett]

On Mon, Jan 04, 2010 at 06:19:19PM -0800, Paul E. McKenney wrote:
> On Mon, Jan 04, 2010 at 06:03:08PM -0800, Josh Triplett wrote:
> > On Mon, Jan 04, 2010 at 04:04:01PM -0800, Paul E. McKenney wrote:
> > > From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > > 
> > > TREE_PREEMPT_RCU maintains an rcu_read_lock_nesting counter in the
> > > task structure, which happens to be a signed int.  So this patch adds a
> > > check for this counter being negative at the end of __rcu_read_unlock().
> > > This check is under CONFIG_PROVE_LOCKING, so can be thought of as being
> > > part of lockdep.
> > > 
> > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > > ---
> > >  kernel/rcutree_plugin.h |    3 +++
> > >  1 files changed, 3 insertions(+), 0 deletions(-)
> > > 
> > > diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
> > > index f11ebd4..e77cdf3 100644
> > > --- a/kernel/rcutree_plugin.h
> > > +++ b/kernel/rcutree_plugin.h
> > > @@ -304,6 +304,9 @@ void __rcu_read_unlock(void)
> > >  	if (--ACCESS_ONCE(t->rcu_read_lock_nesting) == 0 &&
> > >  	    unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
> > >  		rcu_read_unlock_special(t);
> > > +#ifdef CONFIG_PROVE_LOCKING
> > > +	WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0);
> > > +#endif /* #ifdef CONFIG_PROVE_LOCKING */
> > >  }
> > >  EXPORT_SYMBOL_GPL(__rcu_read_unlock);
> > 
> > Given that you *already* need to access t->rcu_read_lock_nesting here,
> > why not just do the test all the time?  Ideally you could access
> > t->rcu_read_lock_nesting once, decrement it, and test for both 0 and
> > negative.
> 
> Because I was paranoid about the extra branch.  Perhaps needlessly
> paranoid, but this is rcu_read_unlock() we are talking about here.  ;-)
> 
> You seem to be suggesting making the first test be "<=", then
> sorting things out later, but given that both the equals-zero and the
> greater-than-zero cases are quite common, I couldn't figure out how to
> avoid the extra test and branch in the common case.  Hence the #ifdef.

No, I think you could simply read the predecremented value into a local
variable, test it once with == 0, then have the WARN_ON_ONCE, and hope
that the compiler figures out it can just test the register once and
then do multiple jumps on the same flags.

You could try it and see what code it generates.

- Josh Triplett

Re: [PATCH tip/core/rcu 2/3] rcu: add debug check for too many rcu_read_unlock()

[Paul E. McKenney]

On Mon, Jan 04, 2010 at 06:28:15PM -0800, Josh Triplett wrote:
> On Mon, Jan 04, 2010 at 06:19:19PM -0800, Paul E. McKenney wrote:
> > On Mon, Jan 04, 2010 at 06:03:08PM -0800, Josh Triplett wrote:
> > > On Mon, Jan 04, 2010 at 04:04:01PM -0800, Paul E. McKenney wrote:
> > > > From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > > > 
> > > > TREE_PREEMPT_RCU maintains an rcu_read_lock_nesting counter in the
> > > > task structure, which happens to be a signed int.  So this patch adds a
> > > > check for this counter being negative at the end of __rcu_read_unlock().
> > > > This check is under CONFIG_PROVE_LOCKING, so can be thought of as being
> > > > part of lockdep.
> > > > 
> > > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > > > ---
> > > >  kernel/rcutree_plugin.h |    3 +++
> > > >  1 files changed, 3 insertions(+), 0 deletions(-)
> > > > 
> > > > diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
> > > > index f11ebd4..e77cdf3 100644
> > > > --- a/kernel/rcutree_plugin.h
> > > > +++ b/kernel/rcutree_plugin.h
> > > > @@ -304,6 +304,9 @@ void __rcu_read_unlock(void)
> > > >  	if (--ACCESS_ONCE(t->rcu_read_lock_nesting) == 0 &&
> > > >  	    unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
> > > >  		rcu_read_unlock_special(t);
> > > > +#ifdef CONFIG_PROVE_LOCKING
> > > > +	WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0);
> > > > +#endif /* #ifdef CONFIG_PROVE_LOCKING */
> > > >  }
> > > >  EXPORT_SYMBOL_GPL(__rcu_read_unlock);
> > > 
> > > Given that you *already* need to access t->rcu_read_lock_nesting here,
> > > why not just do the test all the time?  Ideally you could access
> > > t->rcu_read_lock_nesting once, decrement it, and test for both 0 and
> > > negative.
> > 
> > Because I was paranoid about the extra branch.  Perhaps needlessly
> > paranoid, but this is rcu_read_unlock() we are talking about here.  ;-)
> > 
> > You seem to be suggesting making the first test be "<=", then
> > sorting things out later, but given that both the equals-zero and the
> > greater-than-zero cases are quite common, I couldn't figure out how to
> > avoid the extra test and branch in the common case.  Hence the #ifdef.
> 
> No, I think you could simply read the predecremented value into a local
> variable, test it once with == 0, then have the WARN_ON_ONCE, and hope
> that the compiler figures out it can just test the register once and
> then do multiple jumps on the same flags.
> 
> You could try it and see what code it generates.

I agree that a smart compiler could share condition-code state, but
there still will be the extra branch.  (Keep in mind that this is a
.h file, so #ifdef is permitted -- though I might nevertheless make
a one-line function/macro.)

						Thanx, Paul

Re: [PATCH tip/core/rcu 2/3] rcu: add debug check for too many rcu_read_unlock()

[Josh Triplett]

On Tue, Jan 05, 2010 at 08:21:37AM -0800, Paul E. McKenney wrote:
> On Mon, Jan 04, 2010 at 06:28:15PM -0800, Josh Triplett wrote:
> > On Mon, Jan 04, 2010 at 06:19:19PM -0800, Paul E. McKenney wrote:
> > > On Mon, Jan 04, 2010 at 06:03:08PM -0800, Josh Triplett wrote:
> > > > On Mon, Jan 04, 2010 at 04:04:01PM -0800, Paul E. McKenney wrote:
> > > > > From: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > > > > 
> > > > > TREE_PREEMPT_RCU maintains an rcu_read_lock_nesting counter in the
> > > > > task structure, which happens to be a signed int.  So this patch adds a
> > > > > check for this counter being negative at the end of __rcu_read_unlock().
> > > > > This check is under CONFIG_PROVE_LOCKING, so can be thought of as being
> > > > > part of lockdep.
> > > > > 
> > > > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
> > > > > ---
> > > > >  kernel/rcutree_plugin.h |    3 +++
> > > > >  1 files changed, 3 insertions(+), 0 deletions(-)
> > > > > 
> > > > > diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
> > > > > index f11ebd4..e77cdf3 100644
> > > > > --- a/kernel/rcutree_plugin.h
> > > > > +++ b/kernel/rcutree_plugin.h
> > > > > @@ -304,6 +304,9 @@ void __rcu_read_unlock(void)
> > > > >  	if (--ACCESS_ONCE(t->rcu_read_lock_nesting) == 0 &&
> > > > >  	    unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
> > > > >  		rcu_read_unlock_special(t);
> > > > > +#ifdef CONFIG_PROVE_LOCKING
> > > > > +	WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0);
> > > > > +#endif /* #ifdef CONFIG_PROVE_LOCKING */
> > > > >  }
> > > > >  EXPORT_SYMBOL_GPL(__rcu_read_unlock);
> > > > 
> > > > Given that you *already* need to access t->rcu_read_lock_nesting here,
> > > > why not just do the test all the time?  Ideally you could access
> > > > t->rcu_read_lock_nesting once, decrement it, and test for both 0 and
> > > > negative.
> > > 
> > > Because I was paranoid about the extra branch.  Perhaps needlessly
> > > paranoid, but this is rcu_read_unlock() we are talking about here.  ;-)
> > > 
> > > You seem to be suggesting making the first test be "<=", then
> > > sorting things out later, but given that both the equals-zero and the
> > > greater-than-zero cases are quite common, I couldn't figure out how to
> > > avoid the extra test and branch in the common case.  Hence the #ifdef.
> > 
> > No, I think you could simply read the predecremented value into a local
> > variable, test it once with == 0, then have the WARN_ON_ONCE, and hope
> > that the compiler figures out it can just test the register once and
> > then do multiple jumps on the same flags.
> > 
> > You could try it and see what code it generates.
> 
> I agree that a smart compiler could share condition-code state, but
> there still will be the extra branch.  (Keep in mind that this is a
> .h file, so #ifdef is permitted -- though I might nevertheless make
> a one-line function/macro.)

Hmmm.  Seems like one untaken branch, with unlikely() even, should prove
sufficiently cheap.  But, as you said, this is rcu_read_unlock() we are
talking about here.  ;)

Fair enough; might as well hide it under CONFIG_PROVE_LOCKING, or
perhaps some RCU-specific debugging-related CONFIG symbol.

- Josh Triplett

[tip:core/rcu] rcu: Make MAINTAINERS file match new RCU reality

[tip-bot for Paul E. McKenney]

Commit-ID:  f9094d8e5587cf21091a9516628147c0b55e4264
Gitweb:     http://git.kernel.org/tip/f9094d8e5587cf21091a9516628147c0b55e4264
Author:     Paul E. McKenney <paulmck@linux.vnet.ibm.com>
AuthorDate: Mon, 4 Jan 2010 16:04:00 -0800
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Wed, 13 Jan 2010 09:06:06 +0100

rcu: Make MAINTAINERS file match new RCU reality

Both rcutorture and RCU are supported.  Also, update the files
to match the new layout.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <12626498422334-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 MAINTAINERS |   13 +++++++------
 1 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/MAINTAINERS b/MAINTAINERS
index c8f47bf..175da7c 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -4509,7 +4509,7 @@ F:	drivers/net/wireless/ray*
 RCUTORTURE MODULE
 M:	Josh Triplett <josh@freedesktop.org>
 M:	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
-S:	Maintained
+S:	Supported
 F:	Documentation/RCU/torture.txt
 F:	kernel/rcutorture.c
 
@@ -4534,11 +4534,12 @@ M:	Dipankar Sarma <dipankar@in.ibm.com>
 M:	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
 W:	http://www.rdrop.com/users/paulmck/rclock/
 S:	Supported
-F:	Documentation/RCU/rcu.txt
-F:	Documentation/RCU/rcuref.txt
-F:	include/linux/rcupdate.h
-F:	include/linux/srcu.h
-F:	kernel/rcupdate.c
+F:	Documentation/RCU/
+F:	include/linux/rcu*
+F:	include/linux/srcu*
+F:	kernel/rcu*
+F:	kernel/srcu*
+X:	kernel/rcutorture.c
 
 REAL TIME CLOCK DRIVER
 M:	Paul Gortmaker <p_gortmaker@yahoo.com>

[tip:core/rcu] rcu: Add debug check for too many rcu_read_unlock()

[tip-bot for Paul E. McKenney]

Commit-ID:  cba8244a0f1c277b6b1e48ed6504fa434119e24d
Gitweb:     http://git.kernel.org/tip/cba8244a0f1c277b6b1e48ed6504fa434119e24d
Author:     Paul E. McKenney <paulmck@linux.vnet.ibm.com>
AuthorDate: Mon, 4 Jan 2010 16:04:01 -0800
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Wed, 13 Jan 2010 09:06:06 +0100

rcu: Add debug check for too many rcu_read_unlock()

TREE_PREEMPT_RCU maintains an rcu_read_lock_nesting counter in
the task structure, which happens to be a signed int.  So this
patch adds a check for this counter being negative at the end of
__rcu_read_unlock(). This check is under CONFIG_PROVE_LOCKING,
so can be thought of as being part of lockdep.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <12626498423064-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 kernel/rcutree_plugin.h |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/kernel/rcutree_plugin.h b/kernel/rcutree_plugin.h
index f11ebd4..e77cdf3 100644
--- a/kernel/rcutree_plugin.h
+++ b/kernel/rcutree_plugin.h
@@ -304,6 +304,9 @@ void __rcu_read_unlock(void)
 	if (--ACCESS_ONCE(t->rcu_read_lock_nesting) == 0 &&
 	    unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
 		rcu_read_unlock_special(t);
+#ifdef CONFIG_PROVE_LOCKING
+	WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0);
+#endif /* #ifdef CONFIG_PROVE_LOCKING */
 }
 EXPORT_SYMBOL_GPL(__rcu_read_unlock);
 

[tip:core/rcu] rcu: Give different levels of the rcu_node hierarchy distinct lockdep names

[tip-bot for Paul E. McKenney]

Commit-ID:  b6407e863934965cdc66cbc244d811ceeb6f4d77
Gitweb:     http://git.kernel.org/tip/b6407e863934965cdc66cbc244d811ceeb6f4d77
Author:     Paul E. McKenney <paulmck@linux.vnet.ibm.com>
AuthorDate: Mon, 4 Jan 2010 16:04:02 -0800
Committer:  Ingo Molnar <mingo@elte.hu>
CommitDate: Wed, 13 Jan 2010 09:06:07 +0100

rcu: Give different levels of the rcu_node hierarchy distinct lockdep names

Previously, each level of the rcu_node hierarchy had the same
rather unimaginative name: "&rcu_node_class[i]".  This makes
lockdep diagnostics involving these lockdep classes less helpful
than would be nice. This patch fixes this by giving each level
of the rcu_node hierarchy a distinct name: "rcu_node_level_0",
"rcu_node_level_1", and so on. This version of the patch
includes improved diagnostics suggested by Josh Triplett and
Peter Zijlstra.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <12626498421830-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
 kernel/rcutree.c |    9 ++++++++-
 1 files changed, 8 insertions(+), 1 deletions(-)

diff --git a/kernel/rcutree.c b/kernel/rcutree.c
index 0a4c328..3b13d64 100644
--- a/kernel/rcutree.c
+++ b/kernel/rcutree.c
@@ -1811,11 +1811,17 @@ static void __init rcu_init_levelspread(struct rcu_state *rsp)
  */
 static void __init rcu_init_one(struct rcu_state *rsp)
 {
+	static char *buf[] = { "rcu_node_level_0",
+			       "rcu_node_level_1",
+			       "rcu_node_level_2",
+			       "rcu_node_level_3" };  /* Match MAX_RCU_LVLS */
 	int cpustride = 1;
 	int i;
 	int j;
 	struct rcu_node *rnp;
 
+	BUILD_BUG_ON(MAX_RCU_LVLS > ARRAY_SIZE(buf));  /* Fix buf[] init! */
+
 	/* Initialize the level-tracking arrays. */
 
 	for (i = 1; i < NUM_RCU_LVLS; i++)
@@ -1829,7 +1835,8 @@ static void __init rcu_init_one(struct rcu_state *rsp)
 		rnp = rsp->level[i];
 		for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) {
 			spin_lock_init(&rnp->lock);
-			lockdep_set_class(&rnp->lock, &rcu_node_class[i]);
+			lockdep_set_class_and_name(&rnp->lock,
+						   &rcu_node_class[i], buf[i]);
 			rnp->gpnum = 0;
 			rnp->qsmask = 0;
 			rnp->qsmaskinit = 0;