[PATCH v4 2/7] genirq: Allow global interrupts in request_nmi()

[Mayank Rungta]

request_nmi() currently requires IRQF_PERCPU and forces
IRQF_NOBALANCING. For global system-wide interrupts (such as watchdog
pretimeout SPIs), forcing IRQF_PERCPU sets IRQD_PER_CPU and prevents CPU
hotplug teardown (migrate_one_irq()) from migrating the interrupt off an
offline CPU.

Now that in-flight NMI handlers are synchronized via
__synchronize_nmi(), drop the mandatory IRQF_PERCPU check and stop
forcing IRQF_NOBALANCING in request_nmi() (existing per-CPU callers
already pass both flags explicitly). Also check irq_is_nmi(desc) in
irq_seq_show() (matching kstat_irqs_desc() from commit c09cb1293523
("genirq: Update irq stats from NMI handlers")) so /proc/interrupts
emits per-CPU counts for non-IRQF_PERCPU NMIs.

Signed-off-by: Mayank Rungta <mrungta@xxxxxxxxxx>
---
 kernel/irq/manage.c | 9 +++------
 kernel/irq/proc.c   | 6 ++++--
 2 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 3fb77a2d954d..bd7cf91719d7 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -2352,8 +2352,8 @@ EXPORT_SYMBOL_GPL(request_any_context_irq);
  * An interrupt line delivering NMIs cannot be shared and IRQ handling
  * cannot be threaded.
  *
- * Interrupt lines requested for NMI delivering must produce per cpu
- * interrupts and have auto enabling setting disabled.
+ * Interrupt lines requested for NMI delivering must have auto enabling
+ * setting disabled.
  *
  * @dev_id must be globally unique. Normally the address of the device data
  * structure is used as the cookie. Since the handler receives this value
@@ -2376,9 +2376,6 @@ int request_nmi(unsigned int irq, irq_handler_t handler,
 	if (irqflags & (IRQF_SHARED | IRQF_COND_SUSPEND | IRQF_IRQPOLL))
 		return -EINVAL;
 
-	if (!(irqflags & IRQF_PERCPU))
-		return -EINVAL;
-
 	if (!handler)
 		return -EINVAL;
 
@@ -2396,7 +2393,7 @@ int request_nmi(unsigned int irq, irq_handler_t handler,
 		return -ENOMEM;
 
 	action->handler = handler;
-	action->flags = irqflags | IRQF_NO_THREAD | IRQF_NOBALANCING;
+	action->flags = irqflags | IRQF_NO_THREAD;
 	action->name = name;
 	action->dev_id = dev_id;
 
diff --git a/kernel/irq/proc.c b/kernel/irq/proc.c
index 0c0df16de581..d92f456191e1 100644
--- a/kernel/irq/proc.c
+++ b/kernel/irq/proc.c
@@ -559,10 +559,12 @@ static int irq_seq_show(struct seq_file *p, void *v)
 	seq_putc(p, ':');
 
 	/*
-	 * Always output per CPU interrupts. Output device interrupts only when
-	 * desc::tot_count is not zero.
+	 * Always output per CPU and NMI interrupts, as NMI handlers only
+	 * update per-CPU kstat counters and leave desc::tot_count zero.
+	 * Output other device interrupts only when desc::tot_count is not zero.
 	 */
 	if (irq_settings_is_per_cpu(desc) || irq_settings_is_per_cpu_devid(desc) ||
+	    irq_is_nmi(desc) ||
 	    data_race(desc->tot_count))
 		irq_proc_emit_counts(p, &desc->kstat_irqs->cnt);
 	else
-- 
2.56.0.611.g1030f0b940-goog