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srcu: Move to state-based grace-period sequencing

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The current SRCU grace-period processing might never reach the last
portion of srcu_advance_batches().  This is OK given the current
implementation, as the first portion, up to the try_check_zero()
following the srcu_flip() is sufficient to drive grace periods forward.
However, it has the unfortunate side-effect of making it impossible to
determine when a given grace period has ended, and it will be necessary
to efficiently trace ends of grace periods in order to efficiently handle
per-CPU SRCU callback lists.

This commit therefore adds states to the SRCU grace-period processing,
so that the end of a given SRCU grace period is marked by the transition
to the SRCU_STATE_DONE state.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2017-03-10 15:31:55 -08:00
parent c6e56f593a
commit c2a8ec0778
2 changed files with 64 additions and 47 deletions
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10
include/linux/srcu.h
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@ -48,7 +48,7 @@ struct srcu_struct {
unsigned long completed;
struct srcu_array __percpu *per_cpu_ref;
spinlock_t queue_lock; /* protect ->batch_queue, ->running */
bool running;
int srcu_state;
/* callbacks just queued */
struct rcu_batch batch_queue;
/* callbacks try to do the first check_zero */
@ -62,6 +62,12 @@ struct srcu_struct {
#endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
};
/* Values for -> state variable. */
#define SRCU_STATE_IDLE 0
#define SRCU_STATE_SCAN1 1
#define SRCU_STATE_SCAN2 2
#define SRCU_STATE_DONE 3
#ifdef CONFIG_DEBUG_LOCK_ALLOC
int __init_srcu_struct(struct srcu_struct *sp, const char *name,
@ -89,7 +95,7 @@ void process_srcu(struct work_struct *work);
.completed = -300, \
.per_cpu_ref = &name##_srcu_array, \
.queue_lock = __SPIN_LOCK_UNLOCKED(name.queue_lock), \
.running = false, \
.srcu_state = SRCU_STATE_IDLE, \
.batch_queue = RCU_BATCH_INIT(name.batch_queue), \
.batch_check0 = RCU_BATCH_INIT(name.batch_check0), \
.batch_check1 = RCU_BATCH_INIT(name.batch_check1), \