[PATCHv2] genirq/PM: Make for_each_irq_desc() safe of irq_desc release

Pingfan Liu
2022-04-27T06:04:00Z

First, this is a suspicion of the code, not a really encountered bug.

*** The scenario ***

Two threads involved
threadA "hibernate" runs suspend_device_irqs()
threadB "rcu_cpu_kthread" runs rcu_core()->rcu_do_batch(), which releases
object, let's say irq_desc

Zoom in:
threadA threadB
for_each_irq_desc(irq, desc) {
get irq_descA which is under freeing
--->preempted by rcu_core()->rcu_do_batch() which releases irq_descA
raw_spin_lock_irqsave(&desc->lock, flags);
//Oops

And since in the involved code piece, suspend_device_irqs() runs in a
preemptible context, and there may be more than one thread at this
point. So the preemption can happen.

*** The fix ***

Since there is a blockable synchronize_irq() inside the code piece,
resorting to irq_lock_sparse() to protect the irq_desc from
disappearing.

Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
To: linux-kernel@vger.kernel.org
---
v1 -> v2: improve commit log
kernel/irq/pm.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/kernel/irq/pm.c b/kernel/irq/pm.c
index ca71123a6130..4b67a4c7de3c 100644
--- a/kernel/irq/pm.c
+++ b/kernel/irq/pm.c
@@ -133,6 +133,7 @@ void suspend_device_irqs(void)
struct irq_desc *desc;
int irq;

+ irq_lock_sparse();
for_each_irq_desc(irq, desc) {
unsigned long flags;
bool sync;
@@ -146,6 +147,7 @@ void suspend_device_irqs(void)
if (sync)
synchronize_irq(irq);
}
+ irq_unlock_sparse();
}
EXPORT_SYMBOL_GPL(suspend_device_irqs);

@@ -186,6 +188,7 @@ static void resume_irqs(bool want_early)
struct irq_desc *desc;
int irq;

+ /* The early resume stage is free of irq_desc release */
for_each_irq_desc(irq, desc) {
unsigned long flags;
bool is_early = desc->action &&
--
2.31.1