[PATCH v4] irqchip/riscv-aplic: fix asynchronous probing

[Vladimir Kondratiev]

The APLIC driver leaves probe_type unset, so it follows
PROBE_DEFAULT_STRATEGY and may be probed asynchronously when the
command line requests it. Multiple APLIC instances can therefore
enter aplic_syscore_init() at the same time. The check-then-set of
aplic_syscore_registered is not atomic: two threads can both observe
the flag as false and both call register_syscore(), inserting the
same list node twice. That trips CHECK_DATA_CORRUPTION
("list_add double add") in __list_add_valid_or_report().

The flag is also marked __ro_after_init, but aplic_probe() can run
after init. With MSI, aplic_msi_setup() returns -EPROBE_DEFER while
the MSI parent is not ready, so the later successful probe writes the
flag after it has been made read-only. That write fault exists even
without asynchronous probing.

Replace the flag with an atomic and claim registration with
atomic_cmpxchg(), so only one caller registers the syscore ops and
the store remains writable after init.

Fixes: b330fbfd34d7 ("irqchip/riscv-aplic: Register syscore operations only once")
Signed-off-by: Vladimir Kondratiev <vladimir.kondratiev@xxxxxxxxxxxx>
---
Changes in v4:
- rework commit message
- rebase onto v7.3
- Link to v3: https://lore.kernel.org/r/20261012-aplic-async-probe-v3-1-5cf52dc28690@xxxxxxxxxxxx

Changes in v3:
- drop __ro_after_init attribute due to write to read-only page concern
- Link to v2: https://lore.kernel.org/r/20261012-aplic-async-probe-v2-1-868d7684c9d6@xxxxxxxxxxxx

Changes in v2:
- fixed potential access to read-only page
- Link to v1: https://lore.kernel.org/r/20261012-aplic-async-probe-v1-1-4c2c4f5b0916@xxxxxxxxxxxx

To: Anup Patel <anup@xxxxxxxxxxxxxx>
To: Thomas Gleixner <tglx@xxxxxxxxxx>
To: Radu Rendec <radu@xxxxxxxxxx>
To: Paul Walmsley <pjw@xxxxxxxxxx>
To: Palmer Dabbelt <palmer@xxxxxxxxxxx>
To: Albert Ou <aou@xxxxxxxxxxxxxxxxx>
To: Alexandre Ghiti <alex@xxxxxxxx>
To: Jessica Liu <liu.xuemei1@xxxxxxxxxx>
Cc: linux-riscv@xxxxxxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
---
 drivers/irqchip/irq-riscv-aplic-main.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/irqchip/irq-riscv-aplic-main.c b/drivers/irqchip/irq-riscv-aplic-main.c
index d9afb6ae98cf..54e1d5602f15 100644
--- a/drivers/irqchip/irq-riscv-aplic-main.c
+++ b/drivers/irqchip/irq-riscv-aplic-main.c
@@ -116,14 +116,12 @@ static struct syscore aplic_syscore = {
 	.ops = &aplic_syscore_ops,
 };
 
-static bool aplic_syscore_registered __ro_after_init;
+static atomic_t aplic_syscore_registered = ATOMIC_INIT(0);
 
 static void aplic_syscore_init(void)
 {
-	if (!aplic_syscore_registered) {
+	if (!atomic_cmpxchg(&aplic_syscore_registered, 0, 1))
 		register_syscore(&aplic_syscore);
-		aplic_syscore_registered = true;
-	}
 }
 
 static int aplic_pm_notifier(struct notifier_block *nb, unsigned long action, void *data)

---
base-commit: c03c1a14507dfaf8b856c2608f9ac216021fc222
change-id: 20261012-aplic-async-probe-81624e035607

Best regards,
--  
Vladimir Kondratiev <vladimir.kondratiev@xxxxxxxxxxxx>