[PATCH] rcu/sync: kill rcu_sync_type/gp_type

[PATCH] rcu/sync: kill rcu_sync_type/gp_type

[Oleg Nesterov]

Now that the RCU flavors were consolidated rcu_sync_type makes no sense,
all internal update functions except .held() doesn't depend on gp_type.

The patch adds RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held()) into
rcu_sync_is_idle() because this matches its current user, but probably
we should simply remove this check or introduce rcu_read_lock_any_held().

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
 include/linux/percpu-rwsem.h  |  2 +-
 include/linux/rcu_sync.h      | 32 ++++++-------------------
 kernel/locking/percpu-rwsem.c |  2 +-
 kernel/rcu/sync.c             | 55 ++++---------------------------------------
 4 files changed, 14 insertions(+), 77 deletions(-)

diff --git a/include/linux/percpu-rwsem.h b/include/linux/percpu-rwsem.h
index 03cb4b6..6887636 100644
--- a/include/linux/percpu-rwsem.h
+++ b/include/linux/percpu-rwsem.h
@@ -20,7 +20,7 @@ struct percpu_rw_semaphore {
 #define DEFINE_STATIC_PERCPU_RWSEM(name)				\
 static DEFINE_PER_CPU(unsigned int, __percpu_rwsem_rc_##name);		\
 static struct percpu_rw_semaphore name = {				\
-	.rss = __RCU_SYNC_INITIALIZER(name.rss, RCU_SCHED_SYNC),	\
+	.rss = __RCU_SYNC_INITIALIZER(name.rss),			\
 	.read_count = &__percpu_rwsem_rc_##name,			\
 	.rw_sem = __RWSEM_INITIALIZER(name.rw_sem),			\
 	.writer = __RCUWAIT_INITIALIZER(name.writer),			\
diff --git a/include/linux/rcu_sync.h b/include/linux/rcu_sync.h
index 6fc53a1..e7ae221 100644
--- a/include/linux/rcu_sync.h
+++ b/include/linux/rcu_sync.h
@@ -13,8 +13,6 @@
 #include <linux/wait.h>
 #include <linux/rcupdate.h>
 
-enum rcu_sync_type { RCU_SYNC, RCU_SCHED_SYNC, RCU_BH_SYNC };
-
 /* Structure to mediate between updaters and fastpath-using readers.  */
 struct rcu_sync {
 	int			gp_state;
@@ -23,52 +21,36 @@ struct rcu_sync {
 
 	int			cb_state;
 	struct rcu_head		cb_head;
-
-	enum rcu_sync_type	gp_type;
 };
 
-extern void rcu_sync_lockdep_assert(struct rcu_sync *);
-
 /**
  * rcu_sync_is_idle() - Are readers permitted to use their fastpaths?
  * @rsp: Pointer to rcu_sync structure to use for synchronization
  *
  * Returns true if readers are permitted to use their fastpaths.
- * Must be invoked within an RCU read-side critical section whose
- * flavor matches that of the rcu_sync struture.
+ * Must be invoked within an RCU-sched read-side critical section.
  */
 static inline bool rcu_sync_is_idle(struct rcu_sync *rsp)
 {
-#ifdef CONFIG_PROVE_RCU
-	rcu_sync_lockdep_assert(rsp);
-#endif
+	RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held(),
+			 "suspicious rcu_sync_is_idle() usage");
 	return !rsp->gp_state; /* GP_IDLE */
 }
 
-extern void rcu_sync_init(struct rcu_sync *, enum rcu_sync_type);
+extern void rcu_sync_init(struct rcu_sync *);
 extern void rcu_sync_enter_start(struct rcu_sync *);
 extern void rcu_sync_enter(struct rcu_sync *);
 extern void rcu_sync_exit(struct rcu_sync *);
 extern void rcu_sync_dtor(struct rcu_sync *);
 
-#define __RCU_SYNC_INITIALIZER(name, type) {				\
+#define __RCU_SYNC_INITIALIZER(name) {					\
 		.gp_state = 0,						\
 		.gp_count = 0,						\
 		.gp_wait = __WAIT_QUEUE_HEAD_INITIALIZER(name.gp_wait),	\
 		.cb_state = 0,						\
-		.gp_type = type,					\
 	}
 
-#define	__DEFINE_RCU_SYNC(name, type)	\
-	struct rcu_sync_struct name = __RCU_SYNC_INITIALIZER(name, type)
-
-#define DEFINE_RCU_SYNC(name)		\
-	__DEFINE_RCU_SYNC(name, RCU_SYNC)
-
-#define DEFINE_RCU_SCHED_SYNC(name)	\
-	__DEFINE_RCU_SYNC(name, RCU_SCHED_SYNC)
-
-#define DEFINE_RCU_BH_SYNC(name)	\
-	__DEFINE_RCU_SYNC(name, RCU_BH_SYNC)
+#define	DEFINE_RCU_SYNC(name)	\
+	struct rcu_sync name = __RCU_SYNC_INITIALIZER(name)
 
 #endif /* _LINUX_RCU_SYNC_H_ */
diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index 883cf1b..3784812 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -15,7 +15,7 @@ int __percpu_init_rwsem(struct percpu_rw_semaphore *sem,
 		return -ENOMEM;
 
 	/* ->rw_sem represents the whole percpu_rw_semaphore for lockdep */
-	rcu_sync_init(&sem->rss, RCU_SCHED_SYNC);
+	rcu_sync_init(&sem->rss);
 	__init_rwsem(&sem->rw_sem, name, rwsem_key);
 	rcuwait_init(&sem->writer);
 	sem->readers_block = 0;
diff --git a/kernel/rcu/sync.c b/kernel/rcu/sync.c
index a8304d9..ee427e1 100644
--- a/kernel/rcu/sync.c
+++ b/kernel/rcu/sync.c
@@ -10,65 +10,20 @@
 #include <linux/rcu_sync.h>
 #include <linux/sched.h>
 
-#ifdef CONFIG_PROVE_RCU
-#define __INIT_HELD(func)	.held = func,
-#else
-#define __INIT_HELD(func)
-#endif
-
-static const struct {
-	void (*sync)(void);
-	void (*call)(struct rcu_head *, void (*)(struct rcu_head *));
-	void (*wait)(void);
-#ifdef CONFIG_PROVE_RCU
-	int  (*held)(void);
-#endif
-} gp_ops[] = {
-	[RCU_SYNC] = {
-		.sync = synchronize_rcu,
-		.call = call_rcu,
-		.wait = rcu_barrier,
-		__INIT_HELD(rcu_read_lock_held)
-	},
-	[RCU_SCHED_SYNC] = {
-		.sync = synchronize_rcu,
-		.call = call_rcu,
-		.wait = rcu_barrier,
-		__INIT_HELD(rcu_read_lock_sched_held)
-	},
-	[RCU_BH_SYNC] = {
-		.sync = synchronize_rcu,
-		.call = call_rcu,
-		.wait = rcu_barrier,
-		__INIT_HELD(rcu_read_lock_bh_held)
-	},
-};
-
 enum { GP_IDLE = 0, GP_PENDING, GP_PASSED };
 enum { CB_IDLE = 0, CB_PENDING, CB_REPLAY };
 
 #define	rss_lock	gp_wait.lock
 
-#ifdef CONFIG_PROVE_RCU
-void rcu_sync_lockdep_assert(struct rcu_sync *rsp)
-{
-	RCU_LOCKDEP_WARN(!gp_ops[rsp->gp_type].held(),
-			 "suspicious rcu_sync_is_idle() usage");
-}
-
-EXPORT_SYMBOL_GPL(rcu_sync_lockdep_assert);
-#endif
-
 /**
  * rcu_sync_init() - Initialize an rcu_sync structure
  * @rsp: Pointer to rcu_sync structure to be initialized
  * @type: Flavor of RCU with which to synchronize rcu_sync structure
  */
-void rcu_sync_init(struct rcu_sync *rsp, enum rcu_sync_type type)
+void rcu_sync_init(struct rcu_sync *rsp)
 {
 	memset(rsp, 0, sizeof(*rsp));
 	init_waitqueue_head(&rsp->gp_wait);
-	rsp->gp_type = type;
 }
 
 /**
@@ -114,7 +69,7 @@ void rcu_sync_enter(struct rcu_sync *rsp)
 
 	WARN_ON_ONCE(need_wait && need_sync);
 	if (need_sync) {
-		gp_ops[rsp->gp_type].sync();
+		synchronize_rcu();
 		rsp->gp_state = GP_PASSED;
 		wake_up_all(&rsp->gp_wait);
 	} else if (need_wait) {
@@ -167,7 +122,7 @@ static void rcu_sync_func(struct rcu_head *rhp)
 		 * to catch a later GP.
 		 */
 		rsp->cb_state = CB_PENDING;
-		gp_ops[rsp->gp_type].call(&rsp->cb_head, rcu_sync_func);
+		call_rcu(&rsp->cb_head, rcu_sync_func);
 	} else {
 		/*
 		 * We're at least a GP after rcu_sync_exit(); eveybody will now
@@ -195,7 +150,7 @@ void rcu_sync_exit(struct rcu_sync *rsp)
 	if (!--rsp->gp_count) {
 		if (rsp->cb_state == CB_IDLE) {
 			rsp->cb_state = CB_PENDING;
-			gp_ops[rsp->gp_type].call(&rsp->cb_head, rcu_sync_func);
+			call_rcu(&rsp->cb_head, rcu_sync_func);
 		} else if (rsp->cb_state == CB_PENDING) {
 			rsp->cb_state = CB_REPLAY;
 		}
@@ -220,7 +175,7 @@ void rcu_sync_dtor(struct rcu_sync *rsp)
 	spin_unlock_irq(&rsp->rss_lock);
 
 	if (cb_state != CB_IDLE) {
-		gp_ops[rsp->gp_type].wait();
+		rcu_barrier();
 		WARN_ON_ONCE(rsp->cb_state != CB_IDLE);
 	}
 }
-- 
2.5.0

Re: [PATCH] rcu/sync: kill rcu_sync_type/gp_type

[Paul E. McKenney]

On Tue, Apr 23, 2019 at 02:07:24PM +0200, Oleg Nesterov wrote:
> Now that the RCU flavors were consolidated rcu_sync_type makes no sense,
> all internal update functions except .held() doesn't depend on gp_type.
> 
> The patch adds RCU_LOCKDEP_WARN(!rcu_read_lock_sched_held()) into
> rcu_sync_is_idle() because this matches its current user, but probably
> we should simply remove this check or introduce rcu_read_lock_any_held().
> 
> Signed-off-by: Oleg Nesterov <oleg@redhat.com>

Nice simplification!  Queued for testing and review, thank you!

I wordsmithed the commit log and merged in the RCU-bh and RCU checks
to rcu_sync_is_idle(), with the result shown below.  Does that work
OK, or did I mess something up?

							Thanx, Paul

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

commit cdf54c0ad9951b1f9de63fce5e53a947105b17db
Author: Oleg Nesterov <oleg@redhat.com>
Date:   Tue Apr 23 14:07:24 2019 +0200

    rcu/sync: Kill rcu_sync_type/gp_type
    
    Now that the RCU flavors have been consolidated, rcu_sync_type makes no
    sense because none of internal update functions aside from .held() depend
    on gp_type.  This commit therefore removes this field and consolidates
    the relevant code.
    
    Signed-off-by: Oleg Nesterov <oleg@redhat.com>
    [ paulmck: Added RCU and RCU-bh checks to rcu_sync_is_idle(). ]
    Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>

diff --git a/include/linux/percpu-rwsem.h b/include/linux/percpu-rwsem.h
index 03cb4b6f842e..6887636ea169 100644
--- a/include/linux/percpu-rwsem.h
+++ b/include/linux/percpu-rwsem.h
@@ -20,7 +20,7 @@ struct percpu_rw_semaphore {
 #define DEFINE_STATIC_PERCPU_RWSEM(name)				\
 static DEFINE_PER_CPU(unsigned int, __percpu_rwsem_rc_##name);		\
 static struct percpu_rw_semaphore name = {				\
-	.rss = __RCU_SYNC_INITIALIZER(name.rss, RCU_SCHED_SYNC),	\
+	.rss = __RCU_SYNC_INITIALIZER(name.rss),			\
 	.read_count = &__percpu_rwsem_rc_##name,			\
 	.rw_sem = __RWSEM_INITIALIZER(name.rw_sem),			\
 	.writer = __RCUWAIT_INITIALIZER(name.writer),			\
diff --git a/include/linux/rcu_sync.h b/include/linux/rcu_sync.h
index 6fc53a1345b3..c3326e6c664d 100644
--- a/include/linux/rcu_sync.h
+++ b/include/linux/rcu_sync.h
@@ -13,8 +13,6 @@
 #include <linux/wait.h>
 #include <linux/rcupdate.h>
 
-enum rcu_sync_type { RCU_SYNC, RCU_SCHED_SYNC, RCU_BH_SYNC };
-
 /* Structure to mediate between updaters and fastpath-using readers.  */
 struct rcu_sync {
 	int			gp_state;
@@ -23,52 +21,38 @@ struct rcu_sync {
 
 	int			cb_state;
 	struct rcu_head		cb_head;
-
-	enum rcu_sync_type	gp_type;
 };
 
-extern void rcu_sync_lockdep_assert(struct rcu_sync *);
-
 /**
  * rcu_sync_is_idle() - Are readers permitted to use their fastpaths?
  * @rsp: Pointer to rcu_sync structure to use for synchronization
  *
  * Returns true if readers are permitted to use their fastpaths.
- * Must be invoked within an RCU read-side critical section whose
- * flavor matches that of the rcu_sync struture.
+ * Must be invoked within an RCU-sched read-side critical section.
  */
 static inline bool rcu_sync_is_idle(struct rcu_sync *rsp)
 {
-#ifdef CONFIG_PROVE_RCU
-	rcu_sync_lockdep_assert(rsp);
-#endif
+	RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&
+			 !rcu_read_lock_bh_held() &&
+			 !rcu_read_lock_sched_held(),
+			 "suspicious rcu_sync_is_idle() usage");
 	return !rsp->gp_state; /* GP_IDLE */
 }
 
-extern void rcu_sync_init(struct rcu_sync *, enum rcu_sync_type);
+extern void rcu_sync_init(struct rcu_sync *);
 extern void rcu_sync_enter_start(struct rcu_sync *);
 extern void rcu_sync_enter(struct rcu_sync *);
 extern void rcu_sync_exit(struct rcu_sync *);
 extern void rcu_sync_dtor(struct rcu_sync *);
 
-#define __RCU_SYNC_INITIALIZER(name, type) {				\
+#define __RCU_SYNC_INITIALIZER(name) {					\
 		.gp_state = 0,						\
 		.gp_count = 0,						\
 		.gp_wait = __WAIT_QUEUE_HEAD_INITIALIZER(name.gp_wait),	\
 		.cb_state = 0,						\
-		.gp_type = type,					\
 	}
 
-#define	__DEFINE_RCU_SYNC(name, type)	\
-	struct rcu_sync_struct name = __RCU_SYNC_INITIALIZER(name, type)
-
-#define DEFINE_RCU_SYNC(name)		\
-	__DEFINE_RCU_SYNC(name, RCU_SYNC)
-
-#define DEFINE_RCU_SCHED_SYNC(name)	\
-	__DEFINE_RCU_SYNC(name, RCU_SCHED_SYNC)
-
-#define DEFINE_RCU_BH_SYNC(name)	\
-	__DEFINE_RCU_SYNC(name, RCU_BH_SYNC)
+#define	DEFINE_RCU_SYNC(name)	\
+	struct rcu_sync name = __RCU_SYNC_INITIALIZER(name)
 
 #endif /* _LINUX_RCU_SYNC_H_ */
diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c
index 883cf1b92d90..37848127d50e 100644
--- a/kernel/locking/percpu-rwsem.c
+++ b/kernel/locking/percpu-rwsem.c
@@ -15,7 +15,7 @@ int __percpu_init_rwsem(struct percpu_rw_semaphore *sem,
 		return -ENOMEM;
 
 	/* ->rw_sem represents the whole percpu_rw_semaphore for lockdep */
-	rcu_sync_init(&sem->rss, RCU_SCHED_SYNC);
+	rcu_sync_init(&sem->rss);
 	__init_rwsem(&sem->rw_sem, name, rwsem_key);
 	rcuwait_init(&sem->writer);
 	sem->readers_block = 0;
diff --git a/kernel/rcu/sync.c b/kernel/rcu/sync.c
index a8304d90573f..ee427e138dad 100644
--- a/kernel/rcu/sync.c
+++ b/kernel/rcu/sync.c
@@ -10,65 +10,20 @@
 #include <linux/rcu_sync.h>
 #include <linux/sched.h>
 
-#ifdef CONFIG_PROVE_RCU
-#define __INIT_HELD(func)	.held = func,
-#else
-#define __INIT_HELD(func)
-#endif
-
-static const struct {
-	void (*sync)(void);
-	void (*call)(struct rcu_head *, void (*)(struct rcu_head *));
-	void (*wait)(void);
-#ifdef CONFIG_PROVE_RCU
-	int  (*held)(void);
-#endif
-} gp_ops[] = {
-	[RCU_SYNC] = {
-		.sync = synchronize_rcu,
-		.call = call_rcu,
-		.wait = rcu_barrier,
-		__INIT_HELD(rcu_read_lock_held)
-	},
-	[RCU_SCHED_SYNC] = {
-		.sync = synchronize_rcu,
-		.call = call_rcu,
-		.wait = rcu_barrier,
-		__INIT_HELD(rcu_read_lock_sched_held)
-	},
-	[RCU_BH_SYNC] = {
-		.sync = synchronize_rcu,
-		.call = call_rcu,
-		.wait = rcu_barrier,
-		__INIT_HELD(rcu_read_lock_bh_held)
-	},
-};
-
 enum { GP_IDLE = 0, GP_PENDING, GP_PASSED };
 enum { CB_IDLE = 0, CB_PENDING, CB_REPLAY };
 
 #define	rss_lock	gp_wait.lock
 
-#ifdef CONFIG_PROVE_RCU
-void rcu_sync_lockdep_assert(struct rcu_sync *rsp)
-{
-	RCU_LOCKDEP_WARN(!gp_ops[rsp->gp_type].held(),
-			 "suspicious rcu_sync_is_idle() usage");
-}
-
-EXPORT_SYMBOL_GPL(rcu_sync_lockdep_assert);
-#endif
-
 /**
  * rcu_sync_init() - Initialize an rcu_sync structure
  * @rsp: Pointer to rcu_sync structure to be initialized
  * @type: Flavor of RCU with which to synchronize rcu_sync structure
  */
-void rcu_sync_init(struct rcu_sync *rsp, enum rcu_sync_type type)
+void rcu_sync_init(struct rcu_sync *rsp)
 {
 	memset(rsp, 0, sizeof(*rsp));
 	init_waitqueue_head(&rsp->gp_wait);
-	rsp->gp_type = type;
 }
 
 /**
@@ -114,7 +69,7 @@ void rcu_sync_enter(struct rcu_sync *rsp)
 
 	WARN_ON_ONCE(need_wait && need_sync);
 	if (need_sync) {
-		gp_ops[rsp->gp_type].sync();
+		synchronize_rcu();
 		rsp->gp_state = GP_PASSED;
 		wake_up_all(&rsp->gp_wait);
 	} else if (need_wait) {
@@ -167,7 +122,7 @@ static void rcu_sync_func(struct rcu_head *rhp)
 		 * to catch a later GP.
 		 */
 		rsp->cb_state = CB_PENDING;
-		gp_ops[rsp->gp_type].call(&rsp->cb_head, rcu_sync_func);
+		call_rcu(&rsp->cb_head, rcu_sync_func);
 	} else {
 		/*
 		 * We're at least a GP after rcu_sync_exit(); eveybody will now
@@ -195,7 +150,7 @@ void rcu_sync_exit(struct rcu_sync *rsp)
 	if (!--rsp->gp_count) {
 		if (rsp->cb_state == CB_IDLE) {
 			rsp->cb_state = CB_PENDING;
-			gp_ops[rsp->gp_type].call(&rsp->cb_head, rcu_sync_func);
+			call_rcu(&rsp->cb_head, rcu_sync_func);
 		} else if (rsp->cb_state == CB_PENDING) {
 			rsp->cb_state = CB_REPLAY;
 		}
@@ -220,7 +175,7 @@ void rcu_sync_dtor(struct rcu_sync *rsp)
 	spin_unlock_irq(&rsp->rss_lock);
 
 	if (cb_state != CB_IDLE) {
-		gp_ops[rsp->gp_type].wait();
+		rcu_barrier();
 		WARN_ON_ONCE(rsp->cb_state != CB_IDLE);
 	}
 }

Re: [PATCH] rcu/sync: kill rcu_sync_type/gp_type

[Oleg Nesterov]

On 04/23, Paul E. McKenney wrote:
>
> I wordsmithed the commit log and merged in the RCU-bh and RCU checks
> to rcu_sync_is_idle(), with the result shown below.  Does that work
> OK, or did I mess something up?

Yes, thanks!

the additional RCU-bh and RCU checks matches the "or introduce rcu_read_lock_any_held()"
note from the changelog, perhaps it makes some sense...

Just one nit below,

> - * Must be invoked within an RCU read-side critical section whose
> - * flavor matches that of the rcu_sync struture.
> + * Must be invoked within an RCU-sched read-side critical section.
                                ^^^^^^^^^

Given that the actual code:

>  static inline bool rcu_sync_is_idle(struct rcu_sync *rsp)
>  {
> -#ifdef CONFIG_PROVE_RCU
> -	rcu_sync_lockdep_assert(rsp);
> -#endif
> +	RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&
> +			 !rcu_read_lock_bh_held() &&
> +			 !rcu_read_lock_sched_held(),
> +			 "suspicious rcu_sync_is_idle() usage");

does RCU_LOCKDEP_WARN(!rcu_read_lock_any()) the comment should say

	Must be invoked within an RCU read-side critical section of
	any flavor

?

Oleg.

Re: [PATCH] rcu/sync: kill rcu_sync_type/gp_type

[Paul E. McKenney]

On Wed, Apr 24, 2019 at 01:37:04PM +0200, Oleg Nesterov wrote:
> On 04/23, Paul E. McKenney wrote:
> >
> > I wordsmithed the commit log and merged in the RCU-bh and RCU checks
> > to rcu_sync_is_idle(), with the result shown below.  Does that work
> > OK, or did I mess something up?
> 
> Yes, thanks!
> 
> the additional RCU-bh and RCU checks matches the "or introduce rcu_read_lock_any_held()"
> note from the changelog, perhaps it makes some sense...
> 
> Just one nit below,
> 
> > - * Must be invoked within an RCU read-side critical section whose
> > - * flavor matches that of the rcu_sync struture.
> > + * Must be invoked within an RCU-sched read-side critical section.
>                                 ^^^^^^^^^
> 
> Given that the actual code:
> 
> >  static inline bool rcu_sync_is_idle(struct rcu_sync *rsp)
> >  {
> > -#ifdef CONFIG_PROVE_RCU
> > -	rcu_sync_lockdep_assert(rsp);
> > -#endif
> > +	RCU_LOCKDEP_WARN(!rcu_read_lock_held() &&
> > +			 !rcu_read_lock_bh_held() &&
> > +			 !rcu_read_lock_sched_held(),
> > +			 "suspicious rcu_sync_is_idle() usage");
> 
> does RCU_LOCKDEP_WARN(!rcu_read_lock_any()) the comment should say
> 
> 	Must be invoked within an RCU read-side critical section of
> 	any flavor

Good catch, thank you!  I went with this:

* Must be invoked within some flavor of RCU read-side critical section.

Does that work for you?

							Thanx, Paul

Re: [PATCH] rcu/sync: kill rcu_sync_type/gp_type

[Oleg Nesterov]

On 04/24, Paul E. McKenney wrote:
>
> * Must be invoked within some flavor of RCU read-side critical section.
>
> Does that work for you?

Thanks!

Oleg.