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* [PATCH 1/3] workqueue: Convert for_each_wq to use built-in list check (v2)
@ 2019-08-11 22:11 Joel Fernandes (Google)
  2019-08-11 22:11 ` [PATCH 2/3] doc: Update documentation about list_for_each_entry_rcu (v1) Joel Fernandes (Google)
                   ` (3 more replies)
  0 siblings, 4 replies; 14+ messages in thread
From: Joel Fernandes (Google) @ 2019-08-11 22:11 UTC (permalink / raw)
  To: linux-kernel
  Cc: Joel Fernandes (Google),
	Greg Kroah-Hartman, Jonathan Corbet, Josh Triplett,
	Lai Jiangshan, linux-doc, Mathieu Desnoyers, Paul E. McKenney,
	Rafael J. Wysocki, rcu, Steven Rostedt, Tejun Heo

list_for_each_entry_rcu now has support to check for RCU reader sections
as well as lock. Just use the support in it, instead of explicitly
checking in the caller.

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 kernel/workqueue.c | 10 ++--------
 1 file changed, 2 insertions(+), 8 deletions(-)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 601d61150b65..e882477ebf6e 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -364,11 +364,6 @@ static void workqueue_sysfs_unregister(struct workqueue_struct *wq);
 			 !lockdep_is_held(&wq_pool_mutex),		\
 			 "RCU or wq_pool_mutex should be held")
 
-#define assert_rcu_or_wq_mutex(wq)					\
-	RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&			\
-			 !lockdep_is_held(&wq->mutex),			\
-			 "RCU or wq->mutex should be held")
-
 #define assert_rcu_or_wq_mutex_or_pool_mutex(wq)			\
 	RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&			\
 			 !lockdep_is_held(&wq->mutex) &&		\
@@ -425,9 +420,8 @@ static void workqueue_sysfs_unregister(struct workqueue_struct *wq);
  * ignored.
  */
 #define for_each_pwq(pwq, wq)						\
-	list_for_each_entry_rcu((pwq), &(wq)->pwqs, pwqs_node)		\
-		if (({ assert_rcu_or_wq_mutex(wq); false; })) { }	\
-		else
+	list_for_each_entry_rcu((pwq), &(wq)->pwqs, pwqs_node,		\
+				 lock_is_held(&(wq->mutex).dep_map))
 
 #ifdef CONFIG_DEBUG_OBJECTS_WORK
 
-- 
2.23.0.rc1.153.gdeed80330f-goog


^ permalink raw reply	[flat|nested] 14+ messages in thread

* [PATCH 2/3] doc: Update documentation about list_for_each_entry_rcu (v1)
  2019-08-11 22:11 [PATCH 1/3] workqueue: Convert for_each_wq to use built-in list check (v2) Joel Fernandes (Google)
@ 2019-08-11 22:11 ` Joel Fernandes (Google)
  2019-08-12 20:22   ` Paul E. McKenney
  2019-08-11 22:11 ` [PATCH 3/3] driver/core: Fix build error when SRCU and lockdep disabled Joel Fernandes (Google)
                   ` (2 subsequent siblings)
  3 siblings, 1 reply; 14+ messages in thread
From: Joel Fernandes (Google) @ 2019-08-11 22:11 UTC (permalink / raw)
  To: linux-kernel
  Cc: Joel Fernandes (Google),
	Greg Kroah-Hartman, Jonathan Corbet, Josh Triplett,
	Lai Jiangshan, linux-doc, Mathieu Desnoyers, Paul E. McKenney,
	Rafael J. Wysocki, rcu, Steven Rostedt, Tejun Heo

This patch updates the documentation with information about
usage of lockdep with list_for_each_entry_rcu().

Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
 Documentation/RCU/lockdep.txt   | 15 +++++++++++----
 Documentation/RCU/whatisRCU.txt |  9 ++++++++-
 2 files changed, 19 insertions(+), 5 deletions(-)

diff --git a/Documentation/RCU/lockdep.txt b/Documentation/RCU/lockdep.txt
index da51d3068850..3d967df3a801 100644
--- a/Documentation/RCU/lockdep.txt
+++ b/Documentation/RCU/lockdep.txt
@@ -96,7 +96,14 @@ other flavors of rcu_dereference().  On the other hand, it is illegal
 to use rcu_dereference_protected() if either the RCU-protected pointer
 or the RCU-protected data that it points to can change concurrently.
 
-There are currently only "universal" versions of the rcu_assign_pointer()
-and RCU list-/tree-traversal primitives, which do not (yet) check for
-being in an RCU read-side critical section.  In the future, separate
-versions of these primitives might be created.
+Similar to rcu_dereference_protected, The RCU list and hlist traversal
+primitives also check for whether there are called from within a reader
+section. However, an optional lockdep expression can be passed to them as
+the last argument in case they are called under other non-RCU protection.
+
+For example, the workqueue for_each_pwq() macro is implemented as follows.
+It is safe to call for_each_pwq() outside a reader section but under protection
+of wq->mutex:
+#define for_each_pwq(pwq, wq)
+	list_for_each_entry_rcu((pwq), &(wq)->pwqs, pwqs_node,
+				lock_is_held(&(wq->mutex).dep_map))
diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt
index 17f48319ee16..cdd2a3e10e40 100644
--- a/Documentation/RCU/whatisRCU.txt
+++ b/Documentation/RCU/whatisRCU.txt
@@ -290,7 +290,7 @@ rcu_dereference()
 	at any time, including immediately after the rcu_dereference().
 	And, again like rcu_assign_pointer(), rcu_dereference() is
 	typically used indirectly, via the _rcu list-manipulation
-	primitives, such as list_for_each_entry_rcu().
+	primitives, such as list_for_each_entry_rcu() [2].
 
 	[1] The variant rcu_dereference_protected() can be used outside
 	of an RCU read-side critical section as long as the usage is
@@ -305,6 +305,13 @@ rcu_dereference()
 	a lockdep splat is emitted.  See Documentation/RCU/Design/Requirements/Requirements.rst
 	and the API's code comments for more details and example usage.
 
+	[2] In case the list_for_each_entry_rcu() primitive is intended
+	to be used outside of an RCU reader section such as when
+	protected by a lock, then an additional lockdep expression can be
+	passed as the last argument to it so that RCU lockdep checking code
+	knows that the dereference of the list pointers are safe. If the
+	indicated protection is not provided, a lockdep splat is emitted.
+
 The following diagram shows how each API communicates among the
 reader, updater, and reclaimer.
 
-- 
2.23.0.rc1.153.gdeed80330f-goog


^ permalink raw reply	[flat|nested] 14+ messages in thread

* [PATCH 3/3] driver/core: Fix build error when SRCU and lockdep disabled
  2019-08-11 22:11 [PATCH 1/3] workqueue: Convert for_each_wq to use built-in list check (v2) Joel Fernandes (Google)
  2019-08-11 22:11 ` [PATCH 2/3] doc: Update documentation about list_for_each_entry_rcu (v1) Joel Fernandes (Google)
@ 2019-08-11 22:11 ` Joel Fernandes (Google)
  2019-08-12  5:02   ` Greg Kroah-Hartman
  2019-08-11 22:12 ` [PATCH 1/3] workqueue: Convert for_each_wq to use built-in list check (v2) Joel Fernandes
  2019-08-14 19:48 ` Tejun Heo
  3 siblings, 1 reply; 14+ messages in thread
From: Joel Fernandes (Google) @ 2019-08-11 22:11 UTC (permalink / raw)
  To: linux-kernel
  Cc: Joel Fernandes (Google),
	kbuild test robot, Greg Kroah-Hartman, Jonathan Corbet,
	Josh Triplett, Lai Jiangshan, linux-doc, Mathieu Desnoyers,
	Paul E. McKenney, Rafael J. Wysocki, rcu, Steven Rostedt,
	Tejun Heo

Properly check if lockdep lock checking is disabled at config time. If
so, then lock_is_held() is undefined so don't do any checking.

This fix is similar to the pattern used in srcu_read_lock_held().

Link: https://lore.kernel.org/lkml/201908080026.WSAFx14k%25lkp@intel.com/
Fixes: c9e4d3a2fee8 ("acpi: Use built-in RCU list checking for acpi_ioremaps list")
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
---
This patch is based on the -rcu dev branch.

 drivers/base/core.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 32cf83d1c744..fe25cf690562 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -99,7 +99,11 @@ void device_links_read_unlock(int not_used)
 
 int device_links_read_lock_held(void)
 {
-	return lock_is_held(&device_links_lock);
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+	return lock_is_held(&(device_links_lock.dep_map));
+#else
+	return 1;
+#endif
 }
 #endif /* !CONFIG_SRCU */
 
-- 
2.23.0.rc1.153.gdeed80330f-goog

^ permalink raw reply	[flat|nested] 14+ messages in thread

* Re: [PATCH 1/3] workqueue: Convert for_each_wq to use built-in list check (v2)
  2019-08-11 22:11 [PATCH 1/3] workqueue: Convert for_each_wq to use built-in list check (v2) Joel Fernandes (Google)
  2019-08-11 22:11 ` [PATCH 2/3] doc: Update documentation about list_for_each_entry_rcu (v1) Joel Fernandes (Google)
  2019-08-11 22:11 ` [PATCH 3/3] driver/core: Fix build error when SRCU and lockdep disabled Joel Fernandes (Google)
@ 2019-08-11 22:12 ` Joel Fernandes
  2019-08-14 19:48 ` Tejun Heo
  3 siblings, 0 replies; 14+ messages in thread
From: Joel Fernandes @ 2019-08-11 22:12 UTC (permalink / raw)
  To: LKML
  Cc: Greg Kroah-Hartman, Jonathan Corbet, Josh Triplett,
	Lai Jiangshan, open list:DOCUMENTATION, Mathieu Desnoyers,
	Paul E. McKenney, Rafael J. Wysocki, rcu, Steven Rostedt,
	Tejun Heo

On Sun, Aug 11, 2019 at 6:11 PM Joel Fernandes (Google)
<joel@joelfernandes.org> wrote:
>
> list_for_each_entry_rcu now has support to check for RCU reader sections
> as well as lock. Just use the support in it, instead of explicitly
> checking in the caller.
>
> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>

Tejun,
Could you please Ack this patch? I have resent it here.

Thank you,
- Joel


> ---
>  kernel/workqueue.c | 10 ++--------
>  1 file changed, 2 insertions(+), 8 deletions(-)
>
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 601d61150b65..e882477ebf6e 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -364,11 +364,6 @@ static void workqueue_sysfs_unregister(struct workqueue_struct *wq);
>                          !lockdep_is_held(&wq_pool_mutex),              \
>                          "RCU or wq_pool_mutex should be held")
>
> -#define assert_rcu_or_wq_mutex(wq)                                     \
> -       RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&                       \
> -                        !lockdep_is_held(&wq->mutex),                  \
> -                        "RCU or wq->mutex should be held")
> -
>  #define assert_rcu_or_wq_mutex_or_pool_mutex(wq)                       \
>         RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&                       \
>                          !lockdep_is_held(&wq->mutex) &&                \
> @@ -425,9 +420,8 @@ static void workqueue_sysfs_unregister(struct workqueue_struct *wq);
>   * ignored.
>   */
>  #define for_each_pwq(pwq, wq)                                          \
> -       list_for_each_entry_rcu((pwq), &(wq)->pwqs, pwqs_node)          \
> -               if (({ assert_rcu_or_wq_mutex(wq); false; })) { }       \
> -               else
> +       list_for_each_entry_rcu((pwq), &(wq)->pwqs, pwqs_node,          \
> +                                lock_is_held(&(wq->mutex).dep_map))
>
>  #ifdef CONFIG_DEBUG_OBJECTS_WORK
>
> --
> 2.23.0.rc1.153.gdeed80330f-goog
>

^ permalink raw reply	[flat|nested] 14+ messages in thread

* Re: [PATCH 3/3] driver/core: Fix build error when SRCU and lockdep disabled
  2019-08-11 22:11 ` [PATCH 3/3] driver/core: Fix build error when SRCU and lockdep disabled Joel Fernandes (Google)
@ 2019-08-12  5:02   ` Greg Kroah-Hartman
  2019-08-12 13:03     ` Joel Fernandes
  0 siblings, 1 reply; 14+ messages in thread
From: Greg Kroah-Hartman @ 2019-08-12  5:02 UTC (permalink / raw)
  To: Joel Fernandes (Google)
  Cc: linux-kernel, kbuild test robot, Jonathan Corbet, Josh Triplett,
	Lai Jiangshan, linux-doc, Mathieu Desnoyers, Paul E. McKenney,
	Rafael J. Wysocki, rcu, Steven Rostedt, Tejun Heo

On Sun, Aug 11, 2019 at 06:11:11PM -0400, Joel Fernandes (Google) wrote:
> Properly check if lockdep lock checking is disabled at config time. If
> so, then lock_is_held() is undefined so don't do any checking.
> 
> This fix is similar to the pattern used in srcu_read_lock_held().
> 
> Link: https://lore.kernel.org/lkml/201908080026.WSAFx14k%25lkp@intel.com/
> Fixes: c9e4d3a2fee8 ("acpi: Use built-in RCU list checking for acpi_ioremaps list")

What tree is this commit in?

> Reported-by: kbuild test robot <lkp@intel.com>
> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> ---
> This patch is based on the -rcu dev branch.

Ah...

>  drivers/base/core.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 32cf83d1c744..fe25cf690562 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -99,7 +99,11 @@ void device_links_read_unlock(int not_used)
>  
>  int device_links_read_lock_held(void)
>  {
> -	return lock_is_held(&device_links_lock);
> +#ifdef CONFIG_DEBUG_LOCK_ALLOC
> +	return lock_is_held(&(device_links_lock.dep_map));
> +#else
> +	return 1;
> +#endif

return 1?  So the lock is always held?

confused,

greg k-h

^ permalink raw reply	[flat|nested] 14+ messages in thread

* Re: [PATCH 3/3] driver/core: Fix build error when SRCU and lockdep disabled
  2019-08-12  5:02   ` Greg Kroah-Hartman
@ 2019-08-12 13:03     ` Joel Fernandes
  2019-08-12 18:11       ` Steven Rostedt
  0 siblings, 1 reply; 14+ messages in thread
From: Joel Fernandes @ 2019-08-12 13:03 UTC (permalink / raw)
  To: Greg Kroah-Hartman
  Cc: linux-kernel, kbuild test robot, Jonathan Corbet, Josh Triplett,
	Lai Jiangshan, linux-doc, Mathieu Desnoyers, Paul E. McKenney,
	Rafael J. Wysocki, rcu, Steven Rostedt, Tejun Heo

On Mon, Aug 12, 2019 at 07:02:56AM +0200, Greg Kroah-Hartman wrote:
> On Sun, Aug 11, 2019 at 06:11:11PM -0400, Joel Fernandes (Google) wrote:
> > Properly check if lockdep lock checking is disabled at config time. If
> > so, then lock_is_held() is undefined so don't do any checking.
> > 
> > This fix is similar to the pattern used in srcu_read_lock_held().
> > 
> > Link: https://lore.kernel.org/lkml/201908080026.WSAFx14k%25lkp@intel.com/
> > Fixes: c9e4d3a2fee8 ("acpi: Use built-in RCU list checking for acpi_ioremaps list")
> 
> What tree is this commit in?
> 
> > Reported-by: kbuild test robot <lkp@intel.com>
> > Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> > ---
> > This patch is based on the -rcu dev branch.
> 
> Ah...
> 
> >  drivers/base/core.c | 6 +++++-
> >  1 file changed, 5 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > index 32cf83d1c744..fe25cf690562 100644
> > --- a/drivers/base/core.c
> > +++ b/drivers/base/core.c
> > @@ -99,7 +99,11 @@ void device_links_read_unlock(int not_used)
> >  
> >  int device_links_read_lock_held(void)
> >  {
> > -	return lock_is_held(&device_links_lock);
> > +#ifdef CONFIG_DEBUG_LOCK_ALLOC
> > +	return lock_is_held(&(device_links_lock.dep_map));
> > +#else
> > +	return 1;
> > +#endif
> 
> return 1?  So the lock is always held?

This is just the pattern of an assert that is disabled, so that
false-positives don't happen if lockdep is disabled.

So say someone writes a statement like:
WARN_ON_ONCE(!device_links_read_lock_held());

Since lockdep is disabled, we cannot check whether lock is held or not. Yet,
we don't want false positives by reporting that the lock is not held. In this
case, it is better to report that the lock is held to suppress
false-positives.  srcu_read_lock_held() also follows the same pattern.

thanks,

 - Joel


^ permalink raw reply	[flat|nested] 14+ messages in thread

* Re: [PATCH 3/3] driver/core: Fix build error when SRCU and lockdep disabled
  2019-08-12 13:03     ` Joel Fernandes
@ 2019-08-12 18:11       ` Steven Rostedt
  2019-08-12 20:01         ` Joel Fernandes
  0 siblings, 1 reply; 14+ messages in thread
From: Steven Rostedt @ 2019-08-12 18:11 UTC (permalink / raw)
  To: Joel Fernandes
  Cc: Greg Kroah-Hartman, linux-kernel, kbuild test robot,
	Jonathan Corbet, Josh Triplett, Lai Jiangshan, linux-doc,
	Mathieu Desnoyers, Paul E. McKenney, Rafael J. Wysocki, rcu,
	Tejun Heo

On Mon, 12 Aug 2019 09:03:10 -0400
Joel Fernandes <joel@joelfernandes.org> wrote:

  
> > >  drivers/base/core.c | 6 +++++-
> > >  1 file changed, 5 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > > index 32cf83d1c744..fe25cf690562 100644
> > > --- a/drivers/base/core.c
> > > +++ b/drivers/base/core.c
> > > @@ -99,7 +99,11 @@ void device_links_read_unlock(int not_used)
> > >  
> > >  int device_links_read_lock_held(void)
> > >  {
> > > -	return lock_is_held(&device_links_lock);
> > > +#ifdef CONFIG_DEBUG_LOCK_ALLOC
> > > +	return lock_is_held(&(device_links_lock.dep_map));
> > > +#else
> > > +	return 1;
> > > +#endif  
> > 
> > return 1?  So the lock is always held?  

I was thinking the exact same thing.

> 
> This is just the pattern of an assert that is disabled, so that
> false-positives don't happen if lockdep is disabled.
> 
> So say someone writes a statement like:
> WARN_ON_ONCE(!device_links_read_lock_held());
> 
> Since lockdep is disabled, we cannot check whether lock is held or not. Yet,
> we don't want false positives by reporting that the lock is not held. In this
> case, it is better to report that the lock is held to suppress
> false-positives.  srcu_read_lock_held() also follows the same pattern.
> 

The real answer here is to make that WARN_ON_ONCE() dependent on
lockdep. Something like:


some/header/file.h:

#ifdef CONFIG_DEBUG_LOCK_ALLOC
# define CHECK_DEVICE_LINKS_READ_LOCK_HELD() WARN_ON_ONCE(!defice_links_read_lock_held())
#else
# define CHECK_DEVICE_LINKS_READ_LOCK_HELD() do { } while (0)
#endif

And just use CHECK_DEVICE_LINK_READ_LOCK_HELD() in those places. I
agree with Greg. "device_links_read_lock_heald()" should *never*
blindly return 1. It's confusing.

-- Steve



^ permalink raw reply	[flat|nested] 14+ messages in thread

* Re: [PATCH 3/3] driver/core: Fix build error when SRCU and lockdep disabled
  2019-08-12 18:11       ` Steven Rostedt
@ 2019-08-12 20:01         ` Joel Fernandes
  2019-08-12 20:05           ` Steven Rostedt
  0 siblings, 1 reply; 14+ messages in thread
From: Joel Fernandes @ 2019-08-12 20:01 UTC (permalink / raw)
  To: Steven Rostedt
  Cc: Greg Kroah-Hartman, linux-kernel, kbuild test robot,
	Jonathan Corbet, Josh Triplett, Lai Jiangshan, linux-doc,
	Mathieu Desnoyers, Paul E. McKenney, Rafael J. Wysocki, rcu,
	Tejun Heo

On Mon, Aug 12, 2019 at 02:11:19PM -0400, Steven Rostedt wrote:
> On Mon, 12 Aug 2019 09:03:10 -0400
> Joel Fernandes <joel@joelfernandes.org> wrote:
> 
>   
> > > >  drivers/base/core.c | 6 +++++-
> > > >  1 file changed, 5 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > > > index 32cf83d1c744..fe25cf690562 100644
> > > > --- a/drivers/base/core.c
> > > > +++ b/drivers/base/core.c
> > > > @@ -99,7 +99,11 @@ void device_links_read_unlock(int not_used)
> > > >  
> > > >  int device_links_read_lock_held(void)
> > > >  {
> > > > -	return lock_is_held(&device_links_lock);
> > > > +#ifdef CONFIG_DEBUG_LOCK_ALLOC
> > > > +	return lock_is_held(&(device_links_lock.dep_map));
> > > > +#else
> > > > +	return 1;
> > > > +#endif  
> > > 
> > > return 1?  So the lock is always held?  
> 
> I was thinking the exact same thing.
> 
> > 
> > This is just the pattern of an assert that is disabled, so that
> > false-positives don't happen if lockdep is disabled.
> > 
> > So say someone writes a statement like:
> > WARN_ON_ONCE(!device_links_read_lock_held());
> > 
> > Since lockdep is disabled, we cannot check whether lock is held or not. Yet,
> > we don't want false positives by reporting that the lock is not held. In this
> > case, it is better to report that the lock is held to suppress
> > false-positives.  srcu_read_lock_held() also follows the same pattern.
> > 
> 
> The real answer here is to make that WARN_ON_ONCE() dependent on
> lockdep. Something like:
> 
> 
> some/header/file.h:
> 
> #ifdef CONFIG_DEBUG_LOCK_ALLOC
> # define CHECK_DEVICE_LINKS_READ_LOCK_HELD() WARN_ON_ONCE(!defice_links_read_lock_held())
> #else
> # define CHECK_DEVICE_LINKS_READ_LOCK_HELD() do { } while (0)
> #endif
> 
> And just use CHECK_DEVICE_LINK_READ_LOCK_HELD() in those places. I
> agree with Greg. "device_links_read_lock_heald()" should *never*
> blindly return 1. It's confusing.

Ok, then I will update the patch to do:

#ifdef CONFIG_DEBUG_LOCK_ALLOC
int device_links_read_lock_held(void)
{
	return lock_is_held(&device_links_lock);
}
#endif  

That will also solve the build error. And callers can follow the above pattern you shared.

thanks,

 - Joel


^ permalink raw reply	[flat|nested] 14+ messages in thread

* Re: [PATCH 3/3] driver/core: Fix build error when SRCU and lockdep disabled
  2019-08-12 20:01         ` Joel Fernandes
@ 2019-08-12 20:05           ` Steven Rostedt
  0 siblings, 0 replies; 14+ messages in thread
From: Steven Rostedt @ 2019-08-12 20:05 UTC (permalink / raw)
  To: Joel Fernandes
  Cc: Greg Kroah-Hartman, linux-kernel, kbuild test robot,
	Jonathan Corbet, Josh Triplett, Lai Jiangshan, linux-doc,
	Mathieu Desnoyers, Paul E. McKenney, Rafael J. Wysocki, rcu,
	Tejun Heo

On Mon, 12 Aug 2019 16:01:25 -0400
Joel Fernandes <joel@joelfernandes.org> wrote:

> > some/header/file.h:
> > 
> > #ifdef CONFIG_DEBUG_LOCK_ALLOC
> > # define CHECK_DEVICE_LINKS_READ_LOCK_HELD() WARN_ON_ONCE(!defice_links_read_lock_held())
> > #else
> > # define CHECK_DEVICE_LINKS_READ_LOCK_HELD() do { } while (0)
> > #endif
> > 
> > And just use CHECK_DEVICE_LINK_READ_LOCK_HELD() in those places. I
> > agree with Greg. "device_links_read_lock_heald()" should *never*
> > blindly return 1. It's confusing.  
> 
> Ok, then I will update the patch to do:
> 
> #ifdef CONFIG_DEBUG_LOCK_ALLOC
> int device_links_read_lock_held(void)
> {
> 	return lock_is_held(&device_links_lock);
> }
> #endif  
> 
> That will also solve the build error. And callers can follow the above pattern you shared.

Sounds good!

-- Steve

^ permalink raw reply	[flat|nested] 14+ messages in thread

* Re: [PATCH 2/3] doc: Update documentation about list_for_each_entry_rcu (v1)
  2019-08-11 22:11 ` [PATCH 2/3] doc: Update documentation about list_for_each_entry_rcu (v1) Joel Fernandes (Google)
@ 2019-08-12 20:22   ` Paul E. McKenney
  2019-08-12 20:42     ` Joel Fernandes
  0 siblings, 1 reply; 14+ messages in thread
From: Paul E. McKenney @ 2019-08-12 20:22 UTC (permalink / raw)
  To: Joel Fernandes (Google)
  Cc: linux-kernel, Greg Kroah-Hartman, Jonathan Corbet, Josh Triplett,
	Lai Jiangshan, linux-doc, Mathieu Desnoyers, Rafael J. Wysocki,
	rcu, Steven Rostedt, Tejun Heo

On Sun, Aug 11, 2019 at 06:11:10PM -0400, Joel Fernandes (Google) wrote:
> This patch updates the documentation with information about
> usage of lockdep with list_for_each_entry_rcu().
> 
> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>

Thank you!!!

I queued this for v5.5 with the following wordsmithing.  Please check
to make sure that I didn't mess anything up.

							Thanx, Paul

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

commit d06933df6b5919abfd298291f2a6b0a3a095ae64
Author: Joel Fernandes (Google) <joel@joelfernandes.org>
Date:   Sun Aug 11 18:11:10 2019 -0400

    doc: Update list_for_each_entry_rcu() documentation
    
    This commit updates the documentation with information about
    usage of lockdep with list_for_each_entry_rcu().
    
    Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
    [ paulmck: Wordsmithing. ]
    Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

diff --git a/Documentation/RCU/lockdep.txt b/Documentation/RCU/lockdep.txt
index da51d3068850..89db949eeca0 100644
--- a/Documentation/RCU/lockdep.txt
+++ b/Documentation/RCU/lockdep.txt
@@ -96,7 +96,17 @@ other flavors of rcu_dereference().  On the other hand, it is illegal
 to use rcu_dereference_protected() if either the RCU-protected pointer
 or the RCU-protected data that it points to can change concurrently.
 
-There are currently only "universal" versions of the rcu_assign_pointer()
-and RCU list-/tree-traversal primitives, which do not (yet) check for
-being in an RCU read-side critical section.  In the future, separate
-versions of these primitives might be created.
+Like rcu_dereference(), when lockdep is enabled, RCU list and hlist
+traversal primitives check for being called from within an RCU read-side
+critical section.  However, a lockdep expression can be passed to them
+as a additional optional argument.  With this lockdep expression, these
+traversal primitives will complain only if the lockdep expression is
+false and they are called from outside any RCU read-side critical section.
+
+For example, the workqueue for_each_pwq() macro is intended to be used
+either within an RCU read-side critical section or with wq->mutex held.
+It is thus implemented as follows:
+
+	#define for_each_pwq(pwq, wq)
+		list_for_each_entry_rcu((pwq), &(wq)->pwqs, pwqs_node,
+					lock_is_held(&(wq->mutex).dep_map))
diff --git a/Documentation/RCU/whatisRCU.txt b/Documentation/RCU/whatisRCU.txt
index 17f48319ee16..58ba05c4d97f 100644
--- a/Documentation/RCU/whatisRCU.txt
+++ b/Documentation/RCU/whatisRCU.txt
@@ -290,7 +290,7 @@ rcu_dereference()
 	at any time, including immediately after the rcu_dereference().
 	And, again like rcu_assign_pointer(), rcu_dereference() is
 	typically used indirectly, via the _rcu list-manipulation
-	primitives, such as list_for_each_entry_rcu().
+	primitives, such as list_for_each_entry_rcu() [2].
 
 	[1] The variant rcu_dereference_protected() can be used outside
 	of an RCU read-side critical section as long as the usage is
@@ -305,6 +305,14 @@ rcu_dereference()
 	a lockdep splat is emitted.  See Documentation/RCU/Design/Requirements/Requirements.rst
 	and the API's code comments for more details and example usage.
 
+	[2] If the list_for_each_entry_rcu() instance might be used by
+	update-side code as well as by RCU readers, then an additional
+	lockdep expression can be added to its list of arguments.
+	For example, given an additional "lock_is_held(&mylock)" argument,
+	the RCU lockdep code would complain only if this instance was
+	invoked outside of an RCU read-side critical section and without
+	the protection of mylock.
+
 The following diagram shows how each API communicates among the
 reader, updater, and reclaimer.
 

^ permalink raw reply	[flat|nested] 14+ messages in thread

* Re: [PATCH 2/3] doc: Update documentation about list_for_each_entry_rcu (v1)
  2019-08-12 20:22   ` Paul E. McKenney
@ 2019-08-12 20:42     ` Joel Fernandes
  2019-08-12 21:24       ` Paul E. McKenney
  0 siblings, 1 reply; 14+ messages in thread
From: Joel Fernandes @ 2019-08-12 20:42 UTC (permalink / raw)
  To: Paul E. McKenney
  Cc: linux-kernel, Greg Kroah-Hartman, Jonathan Corbet, Josh Triplett,
	Lai Jiangshan, linux-doc, Mathieu Desnoyers, Rafael J. Wysocki,
	rcu, Steven Rostedt, Tejun Heo

On Mon, Aug 12, 2019 at 01:22:41PM -0700, Paul E. McKenney wrote:
> On Sun, Aug 11, 2019 at 06:11:10PM -0400, Joel Fernandes (Google) wrote:
> > This patch updates the documentation with information about
> > usage of lockdep with list_for_each_entry_rcu().
> > 
> > Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> 
> Thank you!!!
> 
> I queued this for v5.5 with the following wordsmithing.  Please check
> to make sure that I didn't mess anything up.

Yes, this looks great to me. thanks!

Also, I will send out the other drivers/core patch of this series in a bit
with Steve's suggestion.

 - Joel

[snip]

^ permalink raw reply	[flat|nested] 14+ messages in thread

* Re: [PATCH 2/3] doc: Update documentation about list_for_each_entry_rcu (v1)
  2019-08-12 20:42     ` Joel Fernandes
@ 2019-08-12 21:24       ` Paul E. McKenney
  0 siblings, 0 replies; 14+ messages in thread
From: Paul E. McKenney @ 2019-08-12 21:24 UTC (permalink / raw)
  To: Joel Fernandes
  Cc: linux-kernel, Greg Kroah-Hartman, Jonathan Corbet, Josh Triplett,
	Lai Jiangshan, linux-doc, Mathieu Desnoyers, Rafael J. Wysocki,
	rcu, Steven Rostedt, Tejun Heo

On Mon, Aug 12, 2019 at 04:42:05PM -0400, Joel Fernandes wrote:
> On Mon, Aug 12, 2019 at 01:22:41PM -0700, Paul E. McKenney wrote:
> > On Sun, Aug 11, 2019 at 06:11:10PM -0400, Joel Fernandes (Google) wrote:
> > > This patch updates the documentation with information about
> > > usage of lockdep with list_for_each_entry_rcu().
> > > 
> > > Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> > 
> > Thank you!!!
> > 
> > I queued this for v5.5 with the following wordsmithing.  Please check
> > to make sure that I didn't mess anything up.
> 
> Yes, this looks great to me. thanks!
> 
> Also, I will send out the other drivers/core patch of this series in a bit
> with Steve's suggestion.

Very good!  I do need acks from maintainers before sending these upstream,
though.

							Thanx, Paul


^ permalink raw reply	[flat|nested] 14+ messages in thread

* Re: [PATCH 1/3] workqueue: Convert for_each_wq to use built-in list check (v2)
  2019-08-11 22:11 [PATCH 1/3] workqueue: Convert for_each_wq to use built-in list check (v2) Joel Fernandes (Google)
                   ` (2 preceding siblings ...)
  2019-08-11 22:12 ` [PATCH 1/3] workqueue: Convert for_each_wq to use built-in list check (v2) Joel Fernandes
@ 2019-08-14 19:48 ` Tejun Heo
  2019-08-14 22:42   ` Joel Fernandes
  3 siblings, 1 reply; 14+ messages in thread
From: Tejun Heo @ 2019-08-14 19:48 UTC (permalink / raw)
  To: Joel Fernandes (Google)
  Cc: linux-kernel, Greg Kroah-Hartman, Jonathan Corbet, Josh Triplett,
	Lai Jiangshan, linux-doc, Mathieu Desnoyers, Paul E. McKenney,
	Rafael J. Wysocki, rcu, Steven Rostedt

Hello, Joel.

On Sun, Aug 11, 2019 at 06:11:09PM -0400, Joel Fernandes (Google) wrote:
> list_for_each_entry_rcu now has support to check for RCU reader sections
> as well as lock. Just use the support in it, instead of explicitly
> checking in the caller.
> 
> Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>

Acked-by: Tejun Heo <tj@kernel.org>

>  #define for_each_pwq(pwq, wq)						\
> -	list_for_each_entry_rcu((pwq), &(wq)->pwqs, pwqs_node)		\
> -		if (({ assert_rcu_or_wq_mutex(wq); false; })) { }	\
> -		else
> +	list_for_each_entry_rcu((pwq), &(wq)->pwqs, pwqs_node,		\
> +				 lock_is_held(&(wq->mutex).dep_map))

Why not lockdep_is_held() tho?

Thanks.

-- 
tejun

^ permalink raw reply	[flat|nested] 14+ messages in thread

* Re: [PATCH 1/3] workqueue: Convert for_each_wq to use built-in list check (v2)
  2019-08-14 19:48 ` Tejun Heo
@ 2019-08-14 22:42   ` Joel Fernandes
  0 siblings, 0 replies; 14+ messages in thread
From: Joel Fernandes @ 2019-08-14 22:42 UTC (permalink / raw)
  To: Tejun Heo
  Cc: linux-kernel, Greg Kroah-Hartman, Jonathan Corbet, Josh Triplett,
	Lai Jiangshan, linux-doc, Mathieu Desnoyers, Paul E. McKenney,
	Rafael J. Wysocki, rcu, Steven Rostedt

On Wed, Aug 14, 2019 at 12:48:41PM -0700, Tejun Heo wrote:
> Hello, Joel.
> 
> On Sun, Aug 11, 2019 at 06:11:09PM -0400, Joel Fernandes (Google) wrote:
> > list_for_each_entry_rcu now has support to check for RCU reader sections
> > as well as lock. Just use the support in it, instead of explicitly
> > checking in the caller.
> > 
> > Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
> 
> Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

> >  #define for_each_pwq(pwq, wq)						\
> > -	list_for_each_entry_rcu((pwq), &(wq)->pwqs, pwqs_node)		\
> > -		if (({ assert_rcu_or_wq_mutex(wq); false; })) { }	\
> > -		else
> > +	list_for_each_entry_rcu((pwq), &(wq)->pwqs, pwqs_node,		\
> > +				 lock_is_held(&(wq->mutex).dep_map))
> 
> Why not lockdep_is_held() tho?

Yes, that's better.

thanks,

 - Joel


^ permalink raw reply	[flat|nested] 14+ messages in thread

end of thread, back to index

Thread overview: 14+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-08-11 22:11 [PATCH 1/3] workqueue: Convert for_each_wq to use built-in list check (v2) Joel Fernandes (Google)
2019-08-11 22:11 ` [PATCH 2/3] doc: Update documentation about list_for_each_entry_rcu (v1) Joel Fernandes (Google)
2019-08-12 20:22   ` Paul E. McKenney
2019-08-12 20:42     ` Joel Fernandes
2019-08-12 21:24       ` Paul E. McKenney
2019-08-11 22:11 ` [PATCH 3/3] driver/core: Fix build error when SRCU and lockdep disabled Joel Fernandes (Google)
2019-08-12  5:02   ` Greg Kroah-Hartman
2019-08-12 13:03     ` Joel Fernandes
2019-08-12 18:11       ` Steven Rostedt
2019-08-12 20:01         ` Joel Fernandes
2019-08-12 20:05           ` Steven Rostedt
2019-08-11 22:12 ` [PATCH 1/3] workqueue: Convert for_each_wq to use built-in list check (v2) Joel Fernandes
2019-08-14 19:48 ` Tejun Heo
2019-08-14 22:42   ` Joel Fernandes

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