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Subject[RFC][PATCH 4/5] rcusync: Introduce rcu_sync_dtor()
From: Oleg Nesterov <oleg@redhat.com>

Add the new rcu_sync_ops->wait() method and the new helper,
rcu_sync_dtor().

It is needed if you are going to, say, kfree(rcu_sync_object).
It simply calls ops->wait() to "flush" the potentially pending
rcu callback.

Reviewed-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
include/linux/rcusync.h | 1 +
kernel/rcu/sync.c | 22 ++++++++++++++++++++++
2 files changed, 23 insertions(+)

--- a/include/linux/rcusync.h
+++ b/include/linux/rcusync.h
@@ -31,6 +31,7 @@ static inline bool rcu_sync_is_idle(stru
extern void rcu_sync_init(struct rcu_sync_struct *, enum rcu_sync_type);
extern void rcu_sync_enter(struct rcu_sync_struct *);
extern void rcu_sync_exit(struct rcu_sync_struct *);
+extern void rcu_sync_dtor(struct rcu_sync_struct *);

#define __RCU_SYNC_INITIALIZER(name, type) { \
.gp_state = 0, \
--- a/kernel/rcu/sync.c
+++ b/kernel/rcu/sync.c
@@ -10,6 +10,7 @@
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
@@ -17,16 +18,19 @@ static const struct {
[RCU_SYNC] = {
.sync = synchronize_rcu,
.call = call_rcu,
+ .wait = rcu_barrier,
__INIT_HELD(rcu_read_lock_held)
},
[RCU_SCHED_SYNC] = {
.sync = synchronize_sched,
.call = call_rcu_sched,
+ .wait = rcu_barrier_sched,
__INIT_HELD(rcu_read_lock_sched_held)
},
[RCU_BH_SYNC] = {
.sync = synchronize_rcu_bh,
.call = call_rcu_bh,
+ .wait = rcu_barrier_bh,
__INIT_HELD(rcu_read_lock_bh_held)
},
};
@@ -128,3 +132,21 @@ void rcu_sync_exit(struct rcu_sync_struc
}
spin_unlock_irq(&rss->rss_lock);
}
+
+void rcu_sync_dtor(struct rcu_sync_struct *rss)
+{
+ int cb_state;
+
+ BUG_ON(rss->gp_count);
+
+ spin_lock_irq(&rss->rss_lock);
+ if (rss->cb_state == CB_REPLAY)
+ rss->cb_state = CB_PENDING;
+ cb_state = rss->cb_state;
+ spin_unlock_irq(&rss->rss_lock);
+
+ if (cb_state != CB_IDLE) {
+ gp_ops[rss->gp_type].wait();
+ BUG_ON(rss->cb_state != CB_IDLE);
+ }
+}



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