From: Frederic Weisbecker frederic@kernel.org
[ Upstream commit 01b4c39901e087ceebae2733857248de81476bd8 ]
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 Stable-dep-of: 58d766824264 ("tick/nohz: Fix cpu_is_hotpluggable() by checking with nohz subsystem") Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/tick.h | 7 ++++++- include/trace/events/timer.h | 3 ++- kernel/time/tick-sched.c | 7 +++++++ 3 files changed, 15 insertions(+), 2 deletions(-)
diff --git a/include/linux/tick.h b/include/linux/tick.h index 55388ab45fd4d..965163bdfe412 100644 --- a/include/linux/tick.h +++ b/include/linux/tick.h @@ -102,7 +102,8 @@ 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 @@ -110,6 +111,7 @@ 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; @@ -257,6 +259,9 @@ 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 a57e4ee989d62..350b046e7576c 100644 --- a/include/trace/events/timer.h +++ b/include/trace/events/timer.h @@ -362,7 +362,8 @@ 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 48403fb653c2f..7228bdd2eabe2 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -199,6 +199,11 @@ 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; }
@@ -325,6 +330,7 @@ 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) { @@ -332,6 +338,7 @@ 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