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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>
alistair/sunxi64-5.5-dsi
Frederic Weisbecker 2019-07-24 15:22:59 +02:00 committed by Paul E. McKenney
parent 54ecb8f702
commit 01b4c39901
3 changed files with 15 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
include/linux/tick.h
View File

@ -108,7 +108,8 @@ enum tick_dep_bits {
TICK_DEP_BIT_POSIX_TIMER = 0,
TICK_DEP_BIT_PERF_EVENTS = 1,
TICK_DEP_BIT_SCHED = 2,
TICK_DEP_BIT_CLOCK_UNSTABLE = 3
TICK_DEP_BIT_CLOCK_UNSTABLE = 3,
TICK_DEP_BIT_RCU = 4
};
#define TICK_DEP_MASK_NONE 0
@ -116,6 +117,7 @@ enum tick_dep_bits {
#define TICK_DEP_MASK_PERF_EVENTS (1 << TICK_DEP_BIT_PERF_EVENTS)
#define TICK_DEP_MASK_SCHED (1 << TICK_DEP_BIT_SCHED)
#define TICK_DEP_MASK_CLOCK_UNSTABLE (1 << TICK_DEP_BIT_CLOCK_UNSTABLE)
#define TICK_DEP_MASK_RCU (1 << TICK_DEP_BIT_RCU)
#ifdef CONFIG_NO_HZ_COMMON
extern bool tick_nohz_enabled;
@ -268,6 +270,9 @@ static inline bool tick_nohz_full_enabled(void) { return false; }
static inline bool tick_nohz_full_cpu(int cpu) { return false; }
static inline void tick_nohz_full_add_cpus_to(struct cpumask *mask) { }
static inline void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit) { }
static inline void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit) { }
static inline void tick_dep_set(enum tick_dep_bits bit) { }
static inline void tick_dep_clear(enum tick_dep_bits bit) { }
static inline void tick_dep_set_cpu(int cpu, enum tick_dep_bits bit) { }

3
include/trace/events/timer.h
View File

@ -367,7 +367,8 @@ TRACE_EVENT(itimer_expire,
tick_dep_name(POSIX_TIMER) \
tick_dep_name(PERF_EVENTS) \
tick_dep_name(SCHED) \
tick_dep_name_end(CLOCK_UNSTABLE)
tick_dep_name(CLOCK_UNSTABLE) \
tick_dep_name_end(RCU)
#undef tick_dep_name
#undef tick_dep_mask_name

7
kernel/time/tick-sched.c
View File

@ -198,6 +198,11 @@ static bool check_tick_dependency(atomic_t *dep)
return true;
}
if (val & TICK_DEP_MASK_RCU) {
trace_tick_stop(0, TICK_DEP_MASK_RCU);
return true;
}
return false;
}
@ -324,6 +329,7 @@ void tick_nohz_dep_set_cpu(int cpu, enum tick_dep_bits bit)
preempt_enable();
}
}
EXPORT_SYMBOL_GPL(tick_nohz_dep_set_cpu);
void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit)
{
@ -331,6 +337,7 @@ void tick_nohz_dep_clear_cpu(int cpu, enum tick_dep_bits bit)
atomic_andnot(BIT(bit), &ts->tick_dep_mask);
}
EXPORT_SYMBOL_GPL(tick_nohz_dep_clear_cpu);
/*
* Set a per-task tick dependency. Posix CPU timers need this in order to elapse