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rcu: permit rcu_read_unlock() to be called while holding runqueue locks

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Avoid calling into the scheduler while holding core RCU locks.  This
allows rcu_read_unlock() to be called while holding the runqueue locks,
but only as long as there was no chance of the RCU read-side critical
section having been preempted.  (Otherwise, if RCU priority boosting
is enabled, rcu_read_unlock() might call into the scheduler in order to
unboost itself, which might allows self-deadlock on the runqueue locks
within the scheduler.)

Signed-off-by: Paul E. McKenney <paul.mckenney@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
This commit is contained in:
Paul E. McKenney
2011-05-04 21:43:49 -07:00
committed by Paul E. McKenney
parent 29ce831000
commit 1217ed1ba5
3 changed files with 34 additions and 79 deletions
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44
kernel/rcutree.c
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@@ -1133,22 +1133,7 @@ static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
raw_spin_unlock_irqrestore(&rnp->lock, flags);
if (need_report & RCU_OFL_TASKS_EXP_GP)
rcu_report_exp_rnp(rsp, rnp);
/*
* If there are no more online CPUs for this rcu_node structure,
* kill the rcu_node structure's kthread. Otherwise, adjust its
* affinity.
*/
t = rnp->node_kthread_task;
if (t != NULL &&
rnp->qsmaskinit == 0) {
raw_spin_lock_irqsave(&rnp->lock, flags);
rnp->node_kthread_task = NULL;
raw_spin_unlock_irqrestore(&rnp->lock, flags);
kthread_stop(t);
rcu_stop_boost_kthread(rnp);
} else
rcu_node_kthread_setaffinity(rnp, -1);
rcu_node_kthread_setaffinity(rnp, -1);
}
/*
@@ -1320,8 +1305,7 @@ static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *))
return;
}
if (rnp->qsmask == 0) {
rcu_initiate_boost(rnp);
raw_spin_unlock_irqrestore(&rnp->lock, flags);
rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
continue;
}
cpu = rnp->grplo;
@@ -1340,10 +1324,10 @@ static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *))
raw_spin_unlock_irqrestore(&rnp->lock, flags);
}
rnp = rcu_get_root(rsp);
raw_spin_lock_irqsave(&rnp->lock, flags);
if (rnp->qsmask == 0)
rcu_initiate_boost(rnp);
raw_spin_unlock_irqrestore(&rnp->lock, flags);
if (rnp->qsmask == 0) {
raw_spin_lock_irqsave(&rnp->lock, flags);
rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */
}
}
/*
@@ -1497,7 +1481,8 @@ static void invoke_rcu_cpu_kthread(void)
/*
* Wake up the specified per-rcu_node-structure kthread.
* The caller must hold ->lock.
* Because the per-rcu_node kthreads are immortal, we don't need
* to do anything to keep them alive.
*/
static void invoke_rcu_node_kthread(struct rcu_node *rnp)
{
@@ -1546,8 +1531,8 @@ static void rcu_cpu_kthread_timer(unsigned long arg)
raw_spin_lock_irqsave(&rnp->lock, flags);
rnp->wakemask |= rdp->grpmask;
invoke_rcu_node_kthread(rnp);
raw_spin_unlock_irqrestore(&rnp->lock, flags);
invoke_rcu_node_kthread(rnp);
}
/*
@@ -1694,16 +1679,12 @@ static int rcu_node_kthread(void *arg)
for (;;) {
rnp->node_kthread_status = RCU_KTHREAD_WAITING;
wait_event_interruptible(rnp->node_wq, rnp->wakemask != 0 ||
kthread_should_stop());
if (kthread_should_stop())
break;
wait_event_interruptible(rnp->node_wq, rnp->wakemask != 0);
rnp->node_kthread_status = RCU_KTHREAD_RUNNING;
raw_spin_lock_irqsave(&rnp->lock, flags);
mask = rnp->wakemask;
rnp->wakemask = 0;
rcu_initiate_boost(rnp);
raw_spin_unlock_irqrestore(&rnp->lock, flags);
rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */
for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) {
if ((mask & 0x1) == 0)
continue;
@@ -1719,6 +1700,7 @@ static int rcu_node_kthread(void *arg)
preempt_enable();
}
}
/* NOTREACHED */
rnp->node_kthread_status = RCU_KTHREAD_STOPPED;
return 0;
}
@@ -1738,7 +1720,7 @@ static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
int cpu;
unsigned long mask = rnp->qsmaskinit;
if (rnp->node_kthread_task == NULL || mask == 0)
if (rnp->node_kthread_task == NULL)
return;
if (!alloc_cpumask_var(&cm, GFP_KERNEL))
return;