[PATCH v4] riscv: disable local interrupts and stop other CPUs before reboot/shutdown

[Troy Mitchell]

Currently, the RISC-V implementation of machine_restart(), machine_halt(),
and machine_power_off() invokes the kernel teardown chains (e.g.,
do_kernel_restart()) with local interrupts enabled and other CPUs still
running.

This implementation fails to provide a deterministic execution environment
for registered handlers in the restart or power-off notifier chains. These
chains are intended to be executed in a strict atomic and single-threaded
context.

Specifically, under CONFIG_PREEMPT_RCU, rcu_read_lock() does not increment
the preempt_count. If local interrupts remain enabled, the environment
is not guaranteed to be atomic. This can lead to a context misidentification
within generic kernel teardown code, causing it to incorrectly enter
non-atomic paths (such as attempting to acquire sleeping locks), which
results in fatal "scheduling while atomic" splats or system hangs.

Additionally, stopping other CPUs ensures the primary CPU has exclusive
access to the hardware state during the final teardown phase, preventing
unpredictable interference from other active cores.

Align RISC-V with other major architectures by disabling local interrupts
and stopping other CPUs at the beginning of the shutdown sequences. This
guarantees the architectural expectations of the kernel's restart and
power-off handlers are met.

Signed-off-by: Troy Mitchell <troy.mitchell at linux.dev>
Tested-by: Aurelien Jarno <aurelien at aurel32.net>
Tested-by: Anand Moon <linux.amoon at gmail.com>
---
Changes in v4:
- Rebase onto v7.3-rc1.
- Link to v3: https://lore.kernel.org/r/20260330-v7-0-rc1-rv-dis-int-before-restart-v3-1-5a0577fcd136@linux.spacemit.com

Changes in v3:
- add Aurelien's tag
- Link to v2: https://lore.kernel.org/all/20260317-v7-0-rc1-rv-dis-int-before-restart-v2-1-0ecc85fbb7ff@linux.dev/

Changes in v2:
- expand the fix to cover machine_halt() and machine_power_off() for
  architectural consistency.
- update commit message
- Link to v1: https://lore.kernel.org/r/20260311-v7-0-rc1-rv-dis-int-before-restart-v1-1-bc46b4351cac@linux.dev
---
 arch/riscv/kernel/reset.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/riscv/kernel/reset.c b/arch/riscv/kernel/reset.c
index 14eb08a6db85..ec84e3c94a3a 100644
--- a/arch/riscv/kernel/reset.c
+++ b/arch/riscv/kernel/reset.c
@@ -6,6 +6,7 @@
 #include <linux/efi.h>
 #include <linux/reboot.h>
 #include <linux/pm.h>
+#include <linux/smp.h>
 
 static void __noreturn default_power_off(void)
 {
@@ -18,6 +19,9 @@ EXPORT_SYMBOL(pm_power_off);
 
 void machine_restart(char *cmd)
 {
+	local_irq_disable();
+	smp_send_stop();
+
 	/*
 	 * UpdateCapsule() depends on the system being reset via ResetSystem().
 	 */
@@ -30,12 +34,18 @@ void machine_restart(char *cmd)
 
 void machine_halt(void)
 {
+	local_irq_disable();
+	smp_send_stop();
+
 	do_kernel_power_off();
 	default_power_off();
 }
 
 void machine_power_off(void)
 {
+	local_irq_disable();
+	smp_send_stop();
+
 	do_kernel_power_off();
 	default_power_off();
 }

---
base-commit: cee9395acd8043be0644b25c34bfa86623f2b935
change-id: 20260311-v7-0-rc1-rv-dis-int-before-restart-5b3e52a4b419

Best regards,
--  
Troy Mitchell <troy.mitchell at linux.dev>