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rcu: Clear .exp_hint only when deferred quiescent state has been reported

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Currently, the .exp_hint flag is cleared in rcu_read_unlock_special(),
which works, but which can also prevent subsequent rcu_read_unlock() calls
from helping expedite the quiescent state needed by an ongoing expedited
RCU grace period.  This commit therefore defers clearing of .exp_hint
from rcu_read_unlock_special() to rcu_preempt_deferred_qs_irqrestore(),
thus ensuring that intervening calls to rcu_read_unlock() have a chance
to help end the expedited grace period.

Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Lai Jiangshan 2019-11-01 04:06:22 -07:00 committed by Paul E. McKenney
parent c130d2dc93
commit 2eeba5838f
1 changed files with 1 additions and 2 deletions
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3
kernel/rcu/tree_plugin.h
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@ -444,6 +444,7 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
local_irq_restore(flags); local_irq_restore(flags);
return; return;
} }
t->rcu_read_unlock_special.b.exp_hint = false;
t->rcu_read_unlock_special.b.deferred_qs = false; t->rcu_read_unlock_special.b.deferred_qs = false;
if (special.b.need_qs) { if (special.b.need_qs) {
rcu_qs(); rcu_qs();
@ -610,7 +611,6 @@ static void rcu_read_unlock_special(struct task_struct *t)
struct rcu_data *rdp = this_cpu_ptr(&rcu_data); struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
struct rcu_node *rnp = rdp->mynode; struct rcu_node *rnp = rdp->mynode;
t->rcu_read_unlock_special.b.exp_hint = false;
exp = (t->rcu_blocked_node && t->rcu_blocked_node->exp_tasks) || exp = (t->rcu_blocked_node && t->rcu_blocked_node->exp_tasks) ||
(rdp->grpmask & rnp->expmask) || (rdp->grpmask & rnp->expmask) ||
tick_nohz_full_cpu(rdp->cpu); tick_nohz_full_cpu(rdp->cpu);
@ -640,7 +640,6 @@ static void rcu_read_unlock_special(struct task_struct *t)
local_irq_restore(flags); local_irq_restore(flags);
return; return;
} }
WRITE_ONCE(t->rcu_read_unlock_special.b.exp_hint, false);
rcu_preempt_deferred_qs_irqrestore(t, flags); rcu_preempt_deferred_qs_irqrestore(t, flags);
} }