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authorFrederic Weisbecker <frederic@kernel.org>2019-07-24 15:22:59 +0200
committerPaul E. McKenney <paulmck@kernel.org>2019-10-05 19:45:16 +0200
commit01b4c39901e087ceebae2733857248de81476bd8 (patch)
tree72bdea923f0fc822c57b1cc916c596d2bf6682b3
parentLinux 5.4-rc1 (diff)
downloadlinux-01b4c39901e087ceebae2733857248de81476bd8.tar.xz
linux-01b4c39901e087ceebae2733857248de81476bd8.zip
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>
-rw-r--r--include/linux/tick.h7
-rw-r--r--include/trace/events/timer.h3
-rw-r--r--kernel/time/tick-sched.c7
3 files changed, 15 insertions, 2 deletions
diff --git a/include/linux/tick.h b/include/linux/tick.h
index f92a10b5e112..39eb44564058 100644
--- a/include/linux/tick.h
+++ b/include/linux/tick.h
@@ -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) { }
diff --git a/include/trace/events/timer.h b/include/trace/events/timer.h
index b7a904825e7d..295517f109d7 100644
--- a/include/trace/events/timer.h
+++ b/include/trace/events/timer.h
@@ -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
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 955851748dc3..d1b0a84b6112 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -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