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Subject[PATCH 4.19 141/276] irq_work: Do not raise an IPI when queueing work on the local CPU
Date
[ Upstream commit 471ba0e686cb13752bc1ff3216c54b69a2d250ea ]

The QEMU PowerPC/PSeries machine model was not expecting a self-IPI,
and it may be a bit surprising thing to do, so have irq_work_queue_on
do local queueing when target is the current CPU.

Suggested-by: Steven Rostedt <rostedt@goodmis.org>
Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Tested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: =?UTF-8?q?C=C3=A9dric=20Le=20Goater?= <clg@kaod.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: https://lkml.kernel.org/r/20190409093403.20994-1-npiggin@gmail.com
[ Simplified the preprocessor comments.
Fixed unbalanced curly brackets pointed out by Thomas. ]
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
kernel/irq_work.c | 75 ++++++++++++++++++++++++++---------------------
1 file changed, 42 insertions(+), 33 deletions(-)

diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index 6b7cdf17ccf89..73288914ed5e7 100644
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c
@@ -56,61 +56,70 @@ void __weak arch_irq_work_raise(void)
*/
}

-/*
- * Enqueue the irq_work @work on @cpu unless it's already pending
- * somewhere.
- *
- * Can be re-enqueued while the callback is still in progress.
- */
-bool irq_work_queue_on(struct irq_work *work, int cpu)
+/* Enqueue on current CPU, work must already be claimed and preempt disabled */
+static void __irq_work_queue_local(struct irq_work *work)
{
- /* All work should have been flushed before going offline */
- WARN_ON_ONCE(cpu_is_offline(cpu));
-
-#ifdef CONFIG_SMP
-
- /* Arch remote IPI send/receive backend aren't NMI safe */
- WARN_ON_ONCE(in_nmi());
+ /* If the work is "lazy", handle it from next tick if any */
+ if (work->flags & IRQ_WORK_LAZY) {
+ if (llist_add(&work->llnode, this_cpu_ptr(&lazy_list)) &&
+ tick_nohz_tick_stopped())
+ arch_irq_work_raise();
+ } else {
+ if (llist_add(&work->llnode, this_cpu_ptr(&raised_list)))
+ arch_irq_work_raise();
+ }
+}

+/* Enqueue the irq work @work on the current CPU */
+bool irq_work_queue(struct irq_work *work)
+{
/* Only queue if not already pending */
if (!irq_work_claim(work))
return false;

- if (llist_add(&work->llnode, &per_cpu(raised_list, cpu)))
- arch_send_call_function_single_ipi(cpu);
-
-#else /* #ifdef CONFIG_SMP */
- irq_work_queue(work);
-#endif /* #else #ifdef CONFIG_SMP */
+ /* Queue the entry and raise the IPI if needed. */
+ preempt_disable();
+ __irq_work_queue_local(work);
+ preempt_enable();

return true;
}
+EXPORT_SYMBOL_GPL(irq_work_queue);

-/* Enqueue the irq work @work on the current CPU */
-bool irq_work_queue(struct irq_work *work)
+/*
+ * Enqueue the irq_work @work on @cpu unless it's already pending
+ * somewhere.
+ *
+ * Can be re-enqueued while the callback is still in progress.
+ */
+bool irq_work_queue_on(struct irq_work *work, int cpu)
{
+#ifndef CONFIG_SMP
+ return irq_work_queue(work);
+
+#else /* CONFIG_SMP: */
+ /* All work should have been flushed before going offline */
+ WARN_ON_ONCE(cpu_is_offline(cpu));
+
/* Only queue if not already pending */
if (!irq_work_claim(work))
return false;

- /* Queue the entry and raise the IPI if needed. */
preempt_disable();
-
- /* If the work is "lazy", handle it from next tick if any */
- if (work->flags & IRQ_WORK_LAZY) {
- if (llist_add(&work->llnode, this_cpu_ptr(&lazy_list)) &&
- tick_nohz_tick_stopped())
- arch_irq_work_raise();
+ if (cpu != smp_processor_id()) {
+ /* Arch remote IPI send/receive backend aren't NMI safe */
+ WARN_ON_ONCE(in_nmi());
+ if (llist_add(&work->llnode, &per_cpu(raised_list, cpu)))
+ arch_send_call_function_single_ipi(cpu);
} else {
- if (llist_add(&work->llnode, this_cpu_ptr(&raised_list)))
- arch_irq_work_raise();
+ __irq_work_queue_local(work);
}
-
preempt_enable();

return true;
+#endif /* CONFIG_SMP */
}
-EXPORT_SYMBOL_GPL(irq_work_queue);
+

bool irq_work_needs_cpu(void)
{
--
2.20.1


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