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Subject[PATCH RT 3.18] irq_work: Provide a soft-irq based queue
Instead of turning all irq_work requests into lazy ones on -rt, just
move their execution from hard into soft-irq context.

This resolves deadlocks of ftrace which will queue work from arbitrary
contexts, including those that have locks held that are needed for
raising a soft-irq.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
---

Second try, looks much better so far. And it also removes my concerns
regarding other potential cases besides ftrace.

kernel/irq_work.c | 26 ++++++++++----------------
1 file changed, 10 insertions(+), 16 deletions(-)

diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index 9dda38a..3f6ffcd 100644
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c
@@ -85,12 +85,9 @@ bool irq_work_queue_on(struct irq_work *work, int cpu)
raise_irqwork = llist_add(&work->llnode,
&per_cpu(hirq_work_list, cpu));
else
- raise_irqwork = llist_add(&work->llnode,
- &per_cpu(lazy_list, cpu));
-#else
+#endif
raise_irqwork = llist_add(&work->llnode,
&per_cpu(raised_list, cpu));
-#endif

if (raise_irqwork)
arch_send_call_function_single_ipi(cpu);
@@ -114,21 +111,20 @@ bool irq_work_queue(struct irq_work *work)
if (work->flags & IRQ_WORK_HARD_IRQ) {
if (llist_add(&work->llnode, this_cpu_ptr(&hirq_work_list)))
arch_irq_work_raise();
- } else {
+ } else
+#endif
+ if (work->flags & IRQ_WORK_LAZY) {
if (llist_add(&work->llnode, this_cpu_ptr(&lazy_list)) &&
tick_nohz_tick_stopped())
+#ifdef CONFIG_PREEMPT_RT_FULL
raise_softirq(TIMER_SOFTIRQ);
- }
#else
- if (work->flags & IRQ_WORK_LAZY) {
- if (llist_add(&work->llnode, this_cpu_ptr(&lazy_list)) &&
- tick_nohz_tick_stopped())
arch_irq_work_raise();
+#endif
} else {
if (llist_add(&work->llnode, this_cpu_ptr(&raised_list)))
arch_irq_work_raise();
}
-#endif

preempt_enable();

@@ -202,6 +198,8 @@ void irq_work_run(void)
{
#ifdef CONFIG_PREEMPT_RT_FULL
irq_work_run_list(this_cpu_ptr(&hirq_work_list));
+ if (!llist_empty(this_cpu_ptr(&raised_list)))
+ raise_softirq(TIMER_SOFTIRQ);
#else
irq_work_run_list(this_cpu_ptr(&raised_list));
irq_work_run_list(this_cpu_ptr(&lazy_list));
@@ -211,15 +209,11 @@ EXPORT_SYMBOL_GPL(irq_work_run);

void irq_work_tick(void)
{
-#ifdef CONFIG_PREEMPT_RT_FULL
- irq_work_run_list(this_cpu_ptr(&lazy_list));
-#else
- struct llist_head *raised = &__get_cpu_var(raised_list);
+ struct llist_head *raised = this_cpu_ptr(&raised_list);

if (!llist_empty(raised) && !arch_irq_work_has_interrupt())
irq_work_run_list(raised);
- irq_work_run_list(&__get_cpu_var(lazy_list));
-#endif
+ irq_work_run_list(this_cpu_ptr(&lazy_list));
}

/*
--
2.1.4

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