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rcu: Make rcu_read_unlock_special() propagate ->qsmaskinit bit clearing 

This commit causes rcu_read_unlock_special() to propagate ->qsmaskinit
bit clearing up the rcu_node tree once a given rcu_node structure's
blkd_tasks list becomes empty.  This is the final commit in preparation
for the rework of RCU priority boosting:  It enables preempted tasks to
remain queued on their rcu_node structure even after all of that rcu_node
structure's CPUs have gone offline.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney 2014-10-31 12:05:04 -07:00
parent 8af3a5e78c
commit b6a932d1d9
2 changed files with 17 additions and 3 deletions
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4
kernel/rcu/tree.c
View File

@ -2329,6 +2329,10 @@ static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
{
}
static void __maybe_unused rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
{
}
static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
{
}

16
kernel/rcu/tree_plugin.h
View File

@ -322,9 +322,10 @@ static bool rcu_preempt_has_tasks(struct rcu_node *rnp)
*/
void rcu_read_unlock_special(struct task_struct *t)
{
int empty_exp;
int empty_norm;
int empty_exp_now;
bool empty;
bool empty_exp;
bool empty_norm;
bool empty_exp_now;
unsigned long flags;
struct list_head *np;
#ifdef CONFIG_RCU_BOOST
@ -376,6 +377,7 @@ void rcu_read_unlock_special(struct task_struct *t)
break;
raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
}
empty = !rcu_preempt_has_tasks(rnp);
empty_norm = !rcu_preempt_blocked_readers_cgp(rnp);
empty_exp = !rcu_preempted_readers_exp(rnp);
smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
@ -395,6 +397,14 @@ void rcu_read_unlock_special(struct task_struct *t)
drop_boost_mutex = rt_mutex_owner(&rnp->boost_mtx) == t;
#endif /* #ifdef CONFIG_RCU_BOOST */
/*
* If this was the last task on the list, go see if we
* need to propagate ->qsmaskinit bit clearing up the
* rcu_node tree.
*/
if (!empty && !rcu_preempt_has_tasks(rnp))
rcu_cleanup_dead_rnp(rnp);
/*
* If this was the last task on the current list, and if
* we aren't waiting on any CPUs, report the quiescent state.