[PATCH 1/2] irq_work: Reinitialize list heads for secondary CPUs

[Jann Horn]

When printk_deferred() is used before percpu initialization, it will queue
up lazy IRQ work on the boot CPU; percpu initialization then copies the
work list head to all secondary CPUs. To ensure that the secondary CPUs
don't re-execute the boot CPU's work and whatever its ->next pointer leads
to, zero out the secondary CPUs' work list heads before bringing up SMP.

Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>
---
 kernel/irq_work.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/kernel/irq_work.c b/kernel/irq_work.c
index 828cc30774bc..903e5be9aebf 100644
--- a/kernel/irq_work.c
+++ b/kernel/irq_work.c
@@ -152,6 +152,7 @@ static void irq_work_run_list(struct llist_head *list)
 		 * while we are in the middle of the func.
 		 */
 		flags = atomic_fetch_andnot(IRQ_WORK_PENDING, &work->flags);
+		WARN_ON_ONCE((flags & IRQ_WORK_PENDING) == 0);
 
 		work->func(work);
 		/*
@@ -195,3 +196,24 @@ void irq_work_sync(struct irq_work *work)
 		cpu_relax();
 }
 EXPORT_SYMBOL_GPL(irq_work_sync);
+
+/*
+ * If we queued up IRQ work before fully initializing the percpu subsystem, e.g.
+ * via printk_deferred(), the head pointer of the boot CPU will have been copied
+ * over to all the other CPUs.
+ * To fix that, manually initialize the list heads of all secondary processors
+ * before bringing up SMP.
+ */
+static int __init irq_work_percpu_fixup(void)
+{
+	int cpu;
+
+	for_each_possible_cpu(cpu) {
+		if (cpu == smp_processor_id())
+			continue;
+		per_cpu(raised_list.first, cpu) = NULL;
+		per_cpu(lazy_list.first, cpu) = NULL;
+	}
+	return 0;
+}
+early_initcall(irq_work_percpu_fixup)
-- 
2.25.1.696.g5e7596f4ac-goog