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rcu: Force tick on for nohz_full CPUs not reaching quiescent states

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CPUs running for long time periods in the kernel in nohz_full mode
might leave the scheduling-clock interrupt disabled for then full
duration of their in-kernel execution.  This can (among other things)
delay grace periods.  This commit therefore forces the tick back on
for any nohz_full CPU that is failing to pass through a quiescent state
upon return from interrupt, which the resched_cpu() will induce.

Reported-by: Joel Fernandes <joel@joelfernandes.org>
[ paulmck: Clear ->rcu_forced_tick as reported by Joel Fernandes testing. ]
[ paulmck: Apply Joel Fernandes TICK_DEP_MASK_RCU->TICK_DEP_BIT_RCU fix. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2019-08-12 16:14:00 -07:00
parent 79ba7ff5a9
commit 66e4c33b51
2 changed files with 32 additions and 7 deletions
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26
kernel/rcu/tree.c
View File

@ -651,6 +651,12 @@ static __always_inline void rcu_nmi_exit_common(bool irq)
*/
if (rdp->dynticks_nmi_nesting != 1) {
trace_rcu_dyntick(TPS("--="), rdp->dynticks_nmi_nesting, rdp->dynticks_nmi_nesting - 2, rdp->dynticks);
if (tick_nohz_full_cpu(rdp->cpu) &&
rdp->dynticks_nmi_nesting == 2 &&
rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) {
rdp->rcu_forced_tick = true;
tick_dep_set_cpu(rdp->cpu, TICK_DEP_MASK_RCU);
}
WRITE_ONCE(rdp->dynticks_nmi_nesting, /* No store tearing. */
rdp->dynticks_nmi_nesting - 2);
return;
@ -886,6 +892,18 @@ void rcu_irq_enter_irqson(void)
local_irq_restore(flags);
}
/*
* If the scheduler-clock interrupt was enabled on a nohz_full CPU
* in order to get to a quiescent state, disable it.
*/
void rcu_disable_tick_upon_qs(struct rcu_data *rdp)
{
if (tick_nohz_full_cpu(rdp->cpu) && rdp->rcu_forced_tick) {
tick_dep_clear_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
rdp->rcu_forced_tick = false;
}
}
/**
* rcu_is_watching - see if RCU thinks that the current CPU is not idle
*
@ -1980,6 +1998,7 @@ rcu_report_qs_rdp(int cpu, struct rcu_data *rdp)
if (!offloaded)
needwake = rcu_accelerate_cbs(rnp, rdp);
rcu_disable_tick_upon_qs(rdp);
rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
/* ^^^ Released rnp->lock */
if (needwake)
@ -2265,6 +2284,7 @@ static void force_qs_rnp(int (*f)(struct rcu_data *rdp))
int cpu;
unsigned long flags;
unsigned long mask;
struct rcu_data *rdp;
struct rcu_node *rnp;
rcu_for_each_leaf_node(rnp) {
@ -2289,8 +2309,11 @@ static void force_qs_rnp(int (*f)(struct rcu_data *rdp))
for_each_leaf_node_possible_cpu(rnp, cpu) {
unsigned long bit = leaf_node_cpu_bit(rnp, cpu);
if ((rnp->qsmask & bit) != 0) {
if (f(per_cpu_ptr(&rcu_data, cpu)))
rdp = per_cpu_ptr(&rcu_data, cpu);
if (f(rdp)) {
mask |= bit;
rcu_disable_tick_upon_qs(rdp);
}
}
}
if (mask != 0) {
@ -3160,6 +3183,7 @@ void rcu_cpu_starting(unsigned int cpu)
rdp->rcu_onl_gp_seq = READ_ONCE(rcu_state.gp_seq);
rdp->rcu_onl_gp_flags = READ_ONCE(rcu_state.gp_flags);
if (rnp->qsmask & mask) { /* RCU waiting on incoming CPU? */
rcu_disable_tick_upon_qs(rdp);
/* Report QS -after- changing ->qsmaskinitnext! */
rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
} else {

1
kernel/rcu/tree.h
View File

@ -181,6 +181,7 @@ struct rcu_data {
atomic_t dynticks; /* Even value for idle, else odd. */
bool rcu_need_heavy_qs; /* GP old, so heavy quiescent state! */
bool rcu_urgent_qs; /* GP old need light quiescent state. */
bool rcu_forced_tick; /* Forced tick to provide QS. */
#ifdef CONFIG_RCU_FAST_NO_HZ
bool all_lazy; /* All CPU's CBs lazy at idle start? */
unsigned long last_accelerate; /* Last jiffy CBs were accelerated. */