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SubjectRe: [PATCH] rcu/sync: kill rcu_sync_type/gp_type
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);
}
}
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