This is a note to let you know that I've just added the patch titled
nohz: Add TICK_DEP_BIT_RCU
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
nohz-add-tick_dep_bit_rcu.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 620d86a5b9b63b51aa28b67ce64bd56fb90a2fc3
Author: Frederic Weisbecker <frederic@xxxxxxxxxx>
Date: Wed Jul 24 15:22:59 2019 +0200
nohz: Add TICK_DEP_BIT_RCU
[ 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@xxxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Stable-dep-of: 58d766824264 ("tick/nohz: Fix cpu_is_hotpluggable() by checking with nohz subsystem")
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/include/linux/tick.h b/include/linux/tick.h
index f92a10b5e1128..39eb44564058b 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 b7a904825e7df..295517f109d71 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 1b5037ba4ec40..69bdaad4abe17 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -225,6 +225,11 @@ 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;
}
@@ -351,6 +356,7 @@ 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)
{
@@ -358,6 +364,7 @@ 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
