[PATCH] reboot: enable IRQs before do_exit in the halt and power off fallback

[PATCH] reboot: enable IRQs before do_exit in the halt and power off fallback

[Bradley Morgan]

The reboot syscall calls do_exit(0) after kernel_halt() or
kernel_power_off().  Those are expected to stop the machine and not
return.  When they do return (no PM info, power off failed), the
shutdown path has already disabled interrupts: native_machine_shutdown()
calls local_irq_disable() on x86, and do_exit() then hits its
WARN_ON(irqs_disabled()) at kernel/exit.c:930.

do_exit only warns by design; make_task_dead() is the path that fixes
the IRQs disabled state (commit 001c28e57187 ("exit: Detect and fix irq
disabled state in oops")).  The reboot fallback is not an oops and wants
a clean do_exit, so enable IRQs at the two call sites instead, matching
the make_task_dead pattern.

Splat from syzbot:

  ACPI: PM: Preparing to enter system sleep state S5
  kvm: exiting hardware virtualization
  reboot: Power down
  ------------[ cut here ]------------
  irqs_disabled()
  WARNING: kernel/exit.c:930 at do_exit+0x1cf7/0x2ae0 kernel/exit.c:930, CPU#0: init/6193
  CPU: 0 UID: 0 PID: 6193 Comm: init Tainted: G             L      syzkaller #0 PREEMPT(full)
  Tainted: [L]=SOFTLOCKUP
  Call Trace:
   <TASK>
   __do_sys_reboot+0x36e/0x400 kernel/reboot.c:784
   do_syscall_64+0x115/0x840 arch/x86/entry/syscall_64.c:94
   entry_SYSCALL_64_after_hwframe+0x77/0x7f
   </TASK>

Fixes: 001c28e57187 ("exit: Detect and fix irq disabled state in oops")
Reported-by: syzbot+8fdf0d8e10bdde1c2e88@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=8fdf0d8e10bdde1c2e88
Closes: https://lore.kernel.org/all/69f5ec0c.050a0220.312cd3.0023.GAE@google.com/T/
Cc: stable@vger.kernel.org
Signed-off-by: Bradley Morgan <include@grrlz.net>
---
 kernel/reboot.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/kernel/reboot.c b/kernel/reboot.c
index bed6967bfa96..7e8ebb470721 100644
--- a/kernel/reboot.c
+++ b/kernel/reboot.c
@@ -777,10 +777,20 @@ SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd,
 
 	case LINUX_REBOOT_CMD_HALT:
 		kernel_halt();
+		/* kernel_halt() was expected to not return. */
+		if (irqs_disabled()) {
+			pr_info("reboot: halt returned with irqs disabled\n");
+			local_irq_enable();
+		}
 		do_exit(0);
 
 	case LINUX_REBOOT_CMD_POWER_OFF:
 		kernel_power_off();
+		/* kernel_power_off() was expected to not return. */
+		if (irqs_disabled()) {
+			pr_info("reboot: power off returned with irqs disabled\n");
+			local_irq_enable();
+		}
 		do_exit(0);
 		break;
 
-- 
2.53.0

Re: [PATCH] reboot: enable IRQs before do_exit in the halt and power off fallback

[Eric W. Biederman]

Bradley Morgan <include@grrlz.net> writes:

> The reboot syscall calls do_exit(0) after kernel_halt() or
> kernel_power_off().  Those are expected to stop the machine and not
> return.  When they do return (no PM info, power off failed), the
> shutdown path has already disabled interrupts: native_machine_shutdown()
> calls local_irq_disable() on x86, and do_exit() then hits its
> WARN_ON(irqs_disabled()) at kernel/exit.c:930.
>
> do_exit only warns by design; make_task_dead() is the path that fixes
> the IRQs disabled state (commit 001c28e57187 ("exit: Detect and fix irq
> disabled state in oops")).  The reboot fallback is not an oops and wants
> a clean do_exit, so enable IRQs at the two call sites instead, matching
> the make_task_dead pattern.

I think this is fixing symptoms not the actual cause.

How does kernel_halt or kernel_power_off manage to return?

If they aren't supposed to return changing the code to call
make_task_dead to indicate you are on an error path is probably
the better fix.

Eric

> Splat from syzbot:
>
>   ACPI: PM: Preparing to enter system sleep state S5
>   kvm: exiting hardware virtualization
>   reboot: Power down
>   ------------[ cut here ]------------
>   irqs_disabled()
>   WARNING: kernel/exit.c:930 at do_exit+0x1cf7/0x2ae0 kernel/exit.c:930, CPU#0: init/6193
>   CPU: 0 UID: 0 PID: 6193 Comm: init Tainted: G             L      syzkaller #0 PREEMPT(full)
>   Tainted: [L]=SOFTLOCKUP
>   Call Trace:
>    <TASK>
>    __do_sys_reboot+0x36e/0x400 kernel/reboot.c:784
>    do_syscall_64+0x115/0x840 arch/x86/entry/syscall_64.c:94
>    entry_SYSCALL_64_after_hwframe+0x77/0x7f
>    </TASK>
>
> Fixes: 001c28e57187 ("exit: Detect and fix irq disabled state in oops")
> Reported-by: syzbot+8fdf0d8e10bdde1c2e88@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=8fdf0d8e10bdde1c2e88
> Closes: https://lore.kernel.org/all/69f5ec0c.050a0220.312cd3.0023.GAE@google.com/T/
> Cc: stable@vger.kernel.org
> Signed-off-by: Bradley Morgan <include@grrlz.net>
> ---
>  kernel/reboot.c | 10 ++++++++++
>  1 file changed, 10 insertions(+)
>
> diff --git a/kernel/reboot.c b/kernel/reboot.c
> index bed6967bfa96..7e8ebb470721 100644
> --- a/kernel/reboot.c
> +++ b/kernel/reboot.c
> @@ -777,10 +777,20 @@ SYSCALL_DEFINE4(reboot, int, magic1, int, magic2, unsigned int, cmd,
>  
>  	case LINUX_REBOOT_CMD_HALT:
>  		kernel_halt();
> +		/* kernel_halt() was expected to not return. */
> +		if (irqs_disabled()) {
> +			pr_info("reboot: halt returned with irqs disabled\n");
> +			local_irq_enable();
> +		}
>  		do_exit(0);
>  
>  	case LINUX_REBOOT_CMD_POWER_OFF:
>  		kernel_power_off();
> +		/* kernel_power_off() was expected to not return. */
> +		if (irqs_disabled()) {
> +			pr_info("reboot: power off returned with irqs disabled\n");
> +			local_irq_enable();
> +		}
>  		do_exit(0);
>  		break;

Re: [PATCH] reboot: enable IRQs before do_exit in the halt and power off fallback

[Bradley Morgan]

On July 13, 2026 3:54:36 AM GMT+01:00, "Eric W. Biederman"
<ebiederm@xmission.com> wrote:
>Bradley Morgan <include@grrlz.net> writes:
>
>> The reboot syscall calls do_exit(0) after kernel_halt() or
>> kernel_power_off().  Those are expected to stop the machine and not
>> return.  When they do return (no PM info, power off failed), the
>> shutdown path has already disabled interrupts: native_machine_shutdown()
>> calls local_irq_disable() on x86, and do_exit() then hits its
>> WARN_ON(irqs_disabled()) at kernel/exit.c:930.
>>
>> do_exit only warns by design; make_task_dead() is the path that fixes
>> the IRQs disabled state (commit 001c28e57187 ("exit: Detect and fix irq
>> disabled state in oops")).  The reboot fallback is not an oops and wants
>> a clean do_exit, so enable IRQs at the two call sites instead, matching
>> the make_task_dead pattern.
>
>I think this is fixing symptoms not the actual cause.
>
>How does kernel_halt or kernel_power_off manage to return?
>
>If they aren't supposed to return changing the code to call
>make_task_dead to indicate you are on an error path is probably
>the better fix.
>
>Eric

Doh! Nice catch!

I'll do a V2 with some other things I needed to address too, e.g:


>> Splat from syzbot:
>>
>>   ACPI: PM: Preparing to enter system sleep state S5
>>   kvm: exiting hardware virtualization
>>   reboot: Power down
>>   ------------[ cut here ]------------
>>   irqs_disabled()
>>   WARNING: kernel/exit.c:930 at do_exit+0x1cf7/0x2ae0 kernel/exit.c:930,
>CPU#0: init/6193
>>   CPU: 0 UID: 0 PID: 6193 Comm: init Tainted: G             L     
>syzkaller #0 PREEMPT(full)
>>   Tainted: [L]=SOFTLOCKUP
>>   Call Trace:
>>    <TASK>
>>    __do_sys_reboot+0x36e/0x400 kernel/reboot.c:784
>>    do_syscall_64+0x115/0x840 arch/x86/entry/syscall_64.c:94
>>    entry_SYSCALL_64_after_hwframe+0x77/0x7f
>>    </TASK>
>>
>> Fixes: 001c28e57187 ("exit: Detect and fix irq disabled state in oops")
>> Reported-by: syzbot+8fdf0d8e10bdde1c2e88@syzkaller.appspotmail.com
>> Closes: https://syzkaller.appspot.com/bug?extid=8fdf0d8e10bdde1c2e88
>> Closes:
>https://lore.kernel.org/all/69f5ec0c.050a0220.312cd3.0023.GAE@google.com/T/

The lore links wrong, I'll fix that bug later.

>> Cc: stable@vger.kernel.org
>> Signed-off-by: Bradley Morgan <include@grrlz.net>
>> ---
>>  kernel/reboot.c | 10 ++++++++++
>>  1 file changed, 10 insertions(+)
>>
>> diff --git a/kernel/reboot.c b/kernel/reboot.c
>> index bed6967bfa96..7e8ebb470721 100644
>> --- a/kernel/reboot.c
>> +++ b/kernel/reboot.c
>> @@ -777,10 +777,20 @@ SYSCALL_DEFINE4(reboot, int, magic1, int, magic2,
>unsigned int, cmd,
>>  
>>  	case LINUX_REBOOT_CMD_HALT:
>>  		kernel_halt();
>> +		/* kernel_halt() was expected to not return. */
>> +		if (irqs_disabled()) {
>> +			pr_info("reboot: halt returned with irqs disabled\n");
>> +			local_irq_enable();
>> +		}
>>  		do_exit(0);
>>  
>>  	case LINUX_REBOOT_CMD_POWER_OFF:
>>  		kernel_power_off();
>> +		/* kernel_power_off() was expected to not return. */
>> +		if (irqs_disabled()) {
>> +			pr_info("reboot: power off returned with irqs disabled\n");
>> +			local_irq_enable();
>> +		}
>>  		do_exit(0);
>>  		break;
>

Thanks!