diff options
| -rw-r--r-- | arch/x86/entry/common.c | 35 |
1 files changed, 28 insertions, 7 deletions
diff --git a/arch/x86/entry/common.c b/arch/x86/entry/common.c index f4d57782c14b..bd3f14175193 100644 --- a/arch/x86/entry/common.c +++ b/arch/x86/entry/common.c @@ -557,14 +557,34 @@ bool noinstr idtentry_enter_cond_rcu(struct pt_regs *regs) return false; } - if (!__rcu_is_watching()) { + /* + * If this entry hit the idle task invoke rcu_irq_enter() whether + * RCU is watching or not. + * + * Interupts can nest when the first interrupt invokes softirq + * processing on return which enables interrupts. + * + * Scheduler ticks in the idle task can mark quiescent state and + * terminate a grace period, if and only if the timer interrupt is + * not nested into another interrupt. + * + * Checking for __rcu_is_watching() here would prevent the nesting + * interrupt to invoke rcu_irq_enter(). If that nested interrupt is + * the tick then rcu_flavor_sched_clock_irq() would wrongfully + * assume that it is the first interupt and eventually claim + * quiescient state and end grace periods prematurely. + * + * Unconditionally invoke rcu_irq_enter() so RCU state stays + * consistent. + * + * TINY_RCU does not support EQS, so let the compiler eliminate + * this part when enabled. + */ + if (!IS_ENABLED(CONFIG_TINY_RCU) && is_idle_task(current)) { /* * If RCU is not watching then the same careful * sequence vs. lockdep and tracing is required * as in enter_from_user_mode(). - * - * This only happens for IRQs that hit the idle - * loop, i.e. if idle is not using MWAIT. */ lockdep_hardirqs_off(CALLER_ADDR0); rcu_irq_enter(); @@ -576,9 +596,10 @@ bool noinstr idtentry_enter_cond_rcu(struct pt_regs *regs) } /* - * If RCU is watching then RCU only wants to check - * whether it needs to restart the tick in NOHZ - * mode. + * If RCU is watching then RCU only wants to check whether it needs + * to restart the tick in NOHZ mode. rcu_irq_enter_check_tick() + * already contains a warning when RCU is not watching, so no point + * in having another one here. */ instrumentation_begin(); rcu_irq_enter_check_tick(); |