From 01b4c39901e087ceebae2733857248de81476bd8 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Wed, 24 Jul 2019 15:22:59 +0200 Subject: 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 Signed-off-by: Paul E. McKenney --- kernel/time/tick-sched.c | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'kernel/time') 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 -- cgit v1.2.3 From ae9e557b5be2e285f48ee945d9c8faf75d4f6a66 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Fri, 9 Aug 2019 16:29:42 -0700 Subject: time: Export tick start/stop functions for rcutorture It turns out that rcutorture needs to ensure that the scheduling-clock interrupt is enabled in CONFIG_NO_HZ_FULL kernels before starting on CPU-bound in-kernel processing. This commit therefore exports tick_nohz_dep_set_task(), tick_nohz_dep_clear_task(), and tick_nohz_full_setup() to GPL kernel modules. Reported-by: kbuild test robot Signed-off-by: Paul E. McKenney --- kernel/time/tick-sched.c | 4 ++++ 1 file changed, 4 insertions(+) (limited to 'kernel/time') diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index d1b0a84b6112..1ffdb4ba1ded 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -172,6 +172,7 @@ static void tick_sched_handle(struct tick_sched *ts, struct pt_regs *regs) #ifdef CONFIG_NO_HZ_FULL cpumask_var_t tick_nohz_full_mask; bool tick_nohz_full_running; +EXPORT_SYMBOL_GPL(tick_nohz_full_running); static atomic_t tick_dep_mask; static bool check_tick_dependency(atomic_t *dep) @@ -351,11 +352,13 @@ void tick_nohz_dep_set_task(struct task_struct *tsk, enum tick_dep_bits bit) */ tick_nohz_dep_set_all(&tsk->tick_dep_mask, bit); } +EXPORT_SYMBOL_GPL(tick_nohz_dep_set_task); void tick_nohz_dep_clear_task(struct task_struct *tsk, enum tick_dep_bits bit) { atomic_andnot(BIT(bit), &tsk->tick_dep_mask); } +EXPORT_SYMBOL_GPL(tick_nohz_dep_clear_task); /* * Set a per-taskgroup tick dependency. Posix CPU timers need this in order to elapse @@ -404,6 +407,7 @@ void __init tick_nohz_full_setup(cpumask_var_t cpumask) cpumask_copy(tick_nohz_full_mask, cpumask); tick_nohz_full_running = true; } +EXPORT_SYMBOL_GPL(tick_nohz_full_setup); static int tick_nohz_cpu_down(unsigned int cpu) { -- cgit v1.2.3