The following commit has been merged into the core/rcu branch of tip: Commit-ID: 5b14557b073c96a7cf79adc4d7b6c4a8c26b2a43 Gitweb: https://git.kernel.org/tip/5b14557b073c96a7cf79adc4d7b6c4a8c26b2a43 Author: Paul E. McKenney <paulmck@xxxxxxxxxx> AuthorDate: Tue, 26 Nov 2019 18:05:45 -08:00 Committer: Paul E. McKenney <paulmck@xxxxxxxxxx> CommitterDate: Fri, 24 Jan 2020 10:27:33 -08:00 rcu: Avoid tick_dep_set_cpu() misordering In the current code, rcu_nmi_enter_common() might decide to turn on the tick using tick_dep_set_cpu(), but be delayed just before doing so. Then the grace-period kthread might notice that the CPU in question had in fact gone through a quiescent state, thus turning off the tick using tick_dep_clear_cpu(). The later invocation of tick_dep_set_cpu() would then incorrectly leave the tick on. This commit therefore enlists the aid of the leaf rcu_node structure's ->lock to ensure that decisions to enable or disable the tick are carried out before they can be reversed. Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> --- kernel/rcu/tree.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 5445da2..b0e0612 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -800,8 +800,8 @@ void rcu_user_exit(void) */ static __always_inline void rcu_nmi_enter_common(bool irq) { - struct rcu_data *rdp = this_cpu_ptr(&rcu_data); long incby = 2; + struct rcu_data *rdp = this_cpu_ptr(&rcu_data); /* Complain about underflow. */ WARN_ON_ONCE(rdp->dynticks_nmi_nesting < 0); @@ -828,8 +828,13 @@ static __always_inline void rcu_nmi_enter_common(bool irq) } else if (tick_nohz_full_cpu(rdp->cpu) && rdp->dynticks_nmi_nesting == DYNTICK_IRQ_NONIDLE && 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); + raw_spin_lock_rcu_node(rdp->mynode); + // Recheck under lock. + if (rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) { + rdp->rcu_forced_tick = true; + tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU); + } + raw_spin_unlock_rcu_node(rdp->mynode); } trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="), rdp->dynticks_nmi_nesting, @@ -898,6 +903,7 @@ void rcu_irq_enter_irqson(void) */ static void rcu_disable_urgency_upon_qs(struct rcu_data *rdp) { + raw_lockdep_assert_held_rcu_node(rdp->mynode); 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) {
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