nohz: Add TICK_DEP_BIT_RCU
If a nohz_full CPU is looping in the kernel, the scheduling-clock tick might nevertheless remain disabled. In !PREEMPT kernels, this can prevent RCU's attempts to enlist the aid of that CPU's executions of cond_resched(), which can in turn result in an arbitrarily delayed grace period and thus an OOM. RCU therefore needs a way to enable a holdout nohz_full CPU's scheduler-clock interrupt. This commit therefore provides a new TICK_DEP_BIT_RCU value which RCU can pass to tick_dep_set_cpu() and friends to force on the scheduler-clock interrupt for a specified CPU or task. In some cases, rcutorture needs to turn on the scheduler-clock tick, so this commit also exports the relevant symbols to GPL-licensed modules. Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
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@ -108,7 +108,8 @@ enum tick_dep_bits {
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TICK_DEP_BIT_POSIX_TIMER = 0,
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TICK_DEP_BIT_PERF_EVENTS = 1,
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TICK_DEP_BIT_SCHED = 2,
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TICK_DEP_BIT_CLOCK_UNSTABLE = 3
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TICK_DEP_BIT_CLOCK_UNSTABLE = 3,
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TICK_DEP_BIT_RCU = 4
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};
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#define TICK_DEP_MASK_NONE 0
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@ -116,6 +117,7 @@ enum tick_dep_bits {
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#define TICK_DEP_MASK_PERF_EVENTS (1 << TICK_DEP_BIT_PERF_EVENTS)
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#define TICK_DEP_MASK_SCHED (1 << TICK_DEP_BIT_SCHED)
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#define TICK_DEP_MASK_CLOCK_UNSTABLE (1 << TICK_DEP_BIT_CLOCK_UNSTABLE)
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#define TICK_DEP_MASK_RCU (1 << TICK_DEP_BIT_RCU)
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#ifdef CONFIG_NO_HZ_COMMON
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extern bool tick_nohz_enabled;
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@ -268,6 +270,9 @@ static inline bool tick_nohz_full_enabled(void) { return false; }
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static inline bool tick_nohz_full_cpu(int cpu) { return false; }
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static inline void tick_nohz_full_add_cpus_to(struct cpumask *mask) { }
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static inline void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit) { }
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static inline void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit) { }
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static inline void tick_dep_set(enum tick_dep_bits bit) { }
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static inline void tick_dep_clear(enum tick_dep_bits bit) { }
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static inline void tick_dep_set_cpu(int cpu, enum tick_dep_bits bit) { }
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@ -367,7 +367,8 @@ TRACE_EVENT(itimer_expire,
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tick_dep_name(POSIX_TIMER) \
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tick_dep_name(PERF_EVENTS) \
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tick_dep_name(SCHED) \
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tick_dep_name_end(CLOCK_UNSTABLE)
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tick_dep_name(CLOCK_UNSTABLE) \
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tick_dep_name_end(RCU)
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#undef tick_dep_name
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#undef tick_dep_mask_name
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@ -198,6 +198,11 @@ static bool check_tick_dependency(atomic_t *dep)
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return true;
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}
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if (val & TICK_DEP_MASK_RCU) {
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trace_tick_stop(0, TICK_DEP_MASK_RCU);
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return true;
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}
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return false;
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}
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@ -324,6 +329,7 @@ void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit)
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preempt_enable();
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}
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}
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EXPORT_SYMBOL_GPL(tick_nohz_dep_set_cpu);
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void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit)
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{
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@ -331,6 +337,7 @@ void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit)
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atomic_andnot(BIT(bit), &ts->tick_dep_mask);
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}
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EXPORT_SYMBOL_GPL(tick_nohz_dep_clear_cpu);
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/*
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* Set a per-task tick dependency. Posix CPU timers need this in order to elapse
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