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rcu: Improve grace-period start logic
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This commit improves grace-period start logic by checking ->gp_flags
under the lock and by issuing a warning if a grace period is already
in progress.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
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Paul E. McKenney committed Sep 23, 2013
1 parent 272b98c commit f7be820
Showing 1 changed file with 12 additions and 5 deletions.
17 changes: 12 additions & 5 deletions kernel/rcutree.c
Original file line number Diff line number Diff line change
Expand Up @@ -1297,7 +1297,7 @@ static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp)
}

/*
* Initialize a new grace period.
* Initialize a new grace period. Return 0 if no grace period required.
*/
static int rcu_gp_init(struct rcu_state *rsp)
{
Expand All @@ -1306,10 +1306,18 @@ static int rcu_gp_init(struct rcu_state *rsp)

rcu_bind_gp_kthread();
raw_spin_lock_irq(&rnp->lock);
if (rsp->gp_flags == 0) {
/* Spurious wakeup, tell caller to go back to sleep. */
raw_spin_unlock_irq(&rnp->lock);
return 0;
}
rsp->gp_flags = 0; /* Clear all flags: New grace period. */

if (rcu_gp_in_progress(rsp)) {
/* Grace period already in progress, don't start another. */
if (WARN_ON_ONCE(rcu_gp_in_progress(rsp))) {
/*
* Grace period already in progress, don't start another.
* Not supposed to be able to happen.
*/
raw_spin_unlock_irq(&rnp->lock);
return 0;
}
Expand Down Expand Up @@ -1474,8 +1482,7 @@ static int __noreturn rcu_gp_kthread(void *arg)
wait_event_interruptible(rsp->gp_wq,
rsp->gp_flags &
RCU_GP_FLAG_INIT);
if ((rsp->gp_flags & RCU_GP_FLAG_INIT) &&
rcu_gp_init(rsp))
if (rcu_gp_init(rsp))
break;
cond_resched();
flush_signals(current);
Expand Down

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