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Subject[PATCH RT 09/14] irq_work: allow certain work in hard irq context
3.10.32-rt31-rc2 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>

irq_work is processed in softirq context on -RT because we want to avoid
long latencies which might arise from processing lots of perf events.
The noHZ-full mode requires its callback to be called from real hardirq
context (commit 76c24fb ("nohz: New APIs to re-evaluate the tick on full
dynticks CPUs")). If it is called from a thread context we might get
wrong results for checks like "is_idle_task(current)".
This patch introduces a second list (hirq_work_list) which will be used
if irq_work_run() has been invoked from hardirq context and process only
work items marked with IRQ_WORK_HARD_IRQ.

This patch also removes arch_irq_work_raise() from sparc & powerpc like
it is already done for x86. Atleast for powerpc it is somehow
superfluous because it is called from the timer interrupt which should
invoke update_process_times().

Cc: stable-rt@vger.kernel.org
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
arch/powerpc/kernel/time.c | 2 +-
arch/sparc/kernel/pcr.c | 2 ++
include/linux/irq_work.h | 1 +
kernel/irq_work.c | 22 +++++++++++++++++++---
kernel/time/tick-sched.c | 1 +
kernel/timer.c | 2 +-
6 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c
index 5fc29ad..7cc55b2 100644
--- a/arch/powerpc/kernel/time.c
+++ b/arch/powerpc/kernel/time.c
@@ -423,7 +423,7 @@ unsigned long profile_pc(struct pt_regs *regs)
EXPORT_SYMBOL(profile_pc);
#endif

-#ifdef CONFIG_IRQ_WORK
+#if defined(CONFIG_IRQ_WORK) && !defined(CONFIG_PREEMPT_RT_FULL)

/*
* 64-bit uses a byte in the PACA, 32-bit uses a per-cpu variable...
diff --git a/arch/sparc/kernel/pcr.c b/arch/sparc/kernel/pcr.c
index 269af58..dbb51a6 100644
--- a/arch/sparc/kernel/pcr.c
+++ b/arch/sparc/kernel/pcr.c
@@ -43,10 +43,12 @@ void __irq_entry deferred_pcr_work_irq(int irq, struct pt_regs *regs)
set_irq_regs(old_regs);
}

+#ifndef CONFIG_PREEMPT_RT_FULL
void arch_irq_work_raise(void)
{
set_softint(1 << PIL_DEFERRED_PCR_WORK);
}
+#endif

const struct pcr_ops *pcr_ops;
EXPORT_SYMBOL_GPL(pcr_ops);
diff --git a/include/linux/irq_work.h b/include/linux/irq_work.h
index 6601702..60c19ee 100644
--- a/include/linux/irq_work.h
+++ b/include/linux/irq_work.h
@@ -16,6 +16,7 @@
#define IRQ_WORK_BUSY 2UL
#define IRQ_WORK_FLAGS 3UL
#define IRQ_WORK_LAZY 4UL /* Doesn't want IPI, wait for tick */
+#define IRQ_WORK_HARD_IRQ 8UL /* Run hard IRQ context, even on RT */

struct irq_work {
unsigned long flags;
diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index f6e4377..35d21f9 100644
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c
@@ -20,6 +20,9 @@


static DEFINE_PER_CPU(struct llist_head, irq_work_list);
+#ifdef CONFIG_PREEMPT_RT_FULL
+static DEFINE_PER_CPU(struct llist_head, hirq_work_list);
+#endif
static DEFINE_PER_CPU(int, irq_work_raised);

/*
@@ -48,7 +51,11 @@ static bool irq_work_claim(struct irq_work *work)
return true;
}

+#ifdef CONFIG_PREEMPT_RT_FULL
+void arch_irq_work_raise(void)
+#else
void __weak arch_irq_work_raise(void)
+#endif
{
/*
* Lame architectures will get the timer tick callback
@@ -70,8 +77,12 @@ void irq_work_queue(struct irq_work *work)
/* Queue the entry and raise the IPI if needed. */
preempt_disable();

- llist_add(&work->llnode, &__get_cpu_var(irq_work_list));
-
+#ifdef CONFIG_PREEMPT_RT_FULL
+ if (work->flags & IRQ_WORK_HARD_IRQ)
+ llist_add(&work->llnode, &__get_cpu_var(hirq_work_list));
+ else
+#endif
+ llist_add(&work->llnode, &__get_cpu_var(irq_work_list));
/*
* If the work is not "lazy" or the tick is stopped, raise the irq
* work interrupt (if supported by the arch), otherwise, just wait
@@ -115,7 +126,12 @@ static void __irq_work_run(void)
__this_cpu_write(irq_work_raised, 0);
barrier();

- this_list = &__get_cpu_var(irq_work_list);
+#ifdef CONFIG_PREEMPT_RT_FULL
+ if (in_irq())
+ this_list = &__get_cpu_var(hirq_work_list);
+ else
+#endif
+ this_list = &__get_cpu_var(irq_work_list);
if (llist_empty(this_list))
return;

diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 4e657e5..aa1e4b2 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -214,6 +214,7 @@ static void nohz_full_kick_work_func(struct irq_work *work)

static DEFINE_PER_CPU(struct irq_work, nohz_full_kick_work) = {
.func = nohz_full_kick_work_func,
+ .flags = IRQ_WORK_HARD_IRQ,
};

/*
diff --git a/kernel/timer.c b/kernel/timer.c
index f63a793..76846a1 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -1425,7 +1425,7 @@ void update_process_times(int user_tick)
scheduler_tick();
run_local_timers();
rcu_check_callbacks(cpu, user_tick);
-#if defined(CONFIG_IRQ_WORK) && !defined(CONFIG_PREEMPT_RT_FULL)
+#if defined(CONFIG_IRQ_WORK)
if (in_irq())
irq_work_run();
#endif
--
1.8.5.3



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