diff options
| author | Joel Fernandes (Google) <joel@joelfernandes.org> | 2019-09-05 10:26:41 -0700 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2019-10-28 07:02:21 -0700 |
| commit | 516e5ae0c94016294d3ef175454215b235d03945 (patch) | |
| tree | f94a8808e6f86e0287eddf5a1ae77a1bee3a0d6b /kernel/rcu | |
| parent | b200a0489517d9e5a52e983183e890f573454ebd (diff) | |
rcu: Reset CPU hints when reporting a quiescent state
In some cases, tracing shows that need_heavy_qs is still set even though
urgent_qs was cleared upon reporting of a quiescent state. One such
case is when the softirq reports that a CPU has passed quiescent state.
Commit 671a63517cf9 ("rcu: Avoid unnecessary softirq when system is
idle") fixed a bug where core_needs_qs was not being cleared. In order
to avoid running into similar situations with the urgent-grace-period
flags, this commit causes rcu_disable_urgency_upon_qs(), previously
rcu_disable_tick_upon_qs(), to clear the urgency hints, ->rcu_urgent_qs
and ->rcu_need_heavy_qs. Note that it is possible for CPUs to go
offline with these urgency hints still set. This is handled because
rcu_disable_urgency_upon_qs() is also invoked during the online process.
Because these hints can be cleared both by the corresponding CPU and by
the grace-period kthread, this commit also adds a number of READ_ONCE()
and WRITE_ONCE() calls.
Tested overnight with rcutorture running for 60 minutes on all
configurations of RCU.
Signed-off-by: "Joel Fernandes (Google)" <joel@joelfernandes.org>
[ paulmck: Clear urgency flags in rcu_disable_urgency_upon_qs(). ]
[ paulmck: Remove ->core_needs_qs from the set cleared at quiescent state. ]
[ paulmck: Make rcu_disable_urgency_upon_qs static per kbuild test robot. ]
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Diffstat (limited to 'kernel/rcu')
| -rw-r--r-- | kernel/rcu/tree.c | 17 |
1 files changed, 10 insertions, 7 deletions
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 8dc878406c71..82caca305cae 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -827,7 +827,7 @@ static __always_inline void rcu_nmi_enter_common(bool irq) incby = 1; } else if (tick_nohz_full_cpu(rdp->cpu) && rdp->dynticks_nmi_nesting == DYNTICK_IRQ_NONIDLE && - rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) { + READ_ONCE(rdp->rcu_urgent_qs) && !rdp->rcu_forced_tick) { rdp->rcu_forced_tick = true; tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU); } @@ -892,11 +892,14 @@ void rcu_irq_enter_irqson(void) } /* - * If the scheduler-clock interrupt was enabled on a nohz_full CPU - * in order to get to a quiescent state, disable it. + * If any sort of urgency was applied to the current CPU (for example, + * 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) +static void rcu_disable_urgency_upon_qs(struct rcu_data *rdp) { + WRITE_ONCE(rdp->rcu_urgent_qs, false); + WRITE_ONCE(rdp->rcu_need_heavy_qs, false); 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; @@ -1997,7 +2000,7 @@ 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_disable_urgency_upon_qs(rdp); rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags); /* ^^^ Released rnp->lock */ if (needwake) @@ -2311,7 +2314,7 @@ static void force_qs_rnp(int (*f)(struct rcu_data *rdp)) rdp = per_cpu_ptr(&rcu_data, cpu); if (f(rdp)) { mask |= bit; - rcu_disable_tick_upon_qs(rdp); + rcu_disable_urgency_upon_qs(rdp); } } } @@ -3182,7 +3185,7 @@ 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); + rcu_disable_urgency_upon_qs(rdp); /* Report QS -after- changing ->qsmaskinitnext! */ rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags); } else { |