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Subject[PATCH 1/2] irq_work: Reinitialize list heads for secondary CPUs
From
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@google.com>
---
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
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