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authorOleg Nesterov <oleg@redhat.com>2019-04-25 18:50:55 +0200
committerPaul E. McKenney <paulmck@linux.ibm.com>2019-05-28 18:05:23 +0200
commit89da3b94bb97417ca2c5b0ce3a28643819030247 (patch)
tree3a494bdabb013141bbb60f7380b5a0f64d23872b /include
parentlocking/percpu-rwsem: Add DEFINE_PERCPU_RWSEM(), use it to initialize cgroup_... (diff)
downloadlinux-89da3b94bb97417ca2c5b0ce3a28643819030247.tar.xz
linux-89da3b94bb97417ca2c5b0ce3a28643819030247.zip
rcu/sync: Simplify the state machine
With this patch rcu_sync has a single state variable and the transition rules become really simple: GP_IDLE - owned by the first rcu_sync_enter() which moves it to GP_ENTER - owned by rcu-callback which moves it to GP_PASSED - owned by the last rcu_sync_exit() which moves it to GP_EXIT - and this is the only "nontrivial" state. rcu-callback moves it back to GP_IDLE unless another enter() comes before a GP pass. If rcu-callback is invoked before the next rcu_sync_exit() it must see gp_count incremented by that enter() and set GP_PASSED. Otherwise, if the next rcu_sync_exit() wins the race, it will move it to GP_REPLAY - owned by rcu-callback which moves it to GP_EXIT Signed-off-by: Oleg Nesterov <oleg@redhat.com> [ paulmck: While here, apply READ_ONCE() and WRITE_ONCE() to ->gp_state. ] [ paulmck: Tweaks to make htmldocs happy. (Reported by kbuild test robot.) ] Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>
Diffstat (limited to 'include')
-rw-r--r--include/linux/rcu_sync.h4
1 files changed, 1 insertions, 3 deletions
diff --git a/include/linux/rcu_sync.h b/include/linux/rcu_sync.h
index 87971e85519c..9b83865d24f9 100644
--- a/include/linux/rcu_sync.h
+++ b/include/linux/rcu_sync.h
@@ -19,7 +19,6 @@ struct rcu_sync {
int gp_count;
wait_queue_head_t gp_wait;
- int cb_state;
struct rcu_head cb_head;
};
@@ -36,7 +35,7 @@ static inline bool rcu_sync_is_idle(struct rcu_sync *rsp)
!rcu_read_lock_bh_held() &&
!rcu_read_lock_sched_held(),
"suspicious rcu_sync_is_idle() usage");
- return !rsp->gp_state; /* GP_IDLE */
+ return !READ_ONCE(rsp->gp_state); /* GP_IDLE */
}
extern void rcu_sync_init(struct rcu_sync *);
@@ -49,7 +48,6 @@ extern void rcu_sync_dtor(struct rcu_sync *);
.gp_state = 0, \
.gp_count = 0, \
.gp_wait = __WAIT_QUEUE_HEAD_INITIALIZER(name.gp_wait), \
- .cb_state = 0, \
}
#define DEFINE_RCU_SYNC(name) \