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@xxxxxxxxxxxx> wrote:
>Bradley Morgan <include@xxxxxxxxx> 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@xxxxxxxxxxxxxxxxxxxxxxxxx
>> Closes: https://syzkaller.appspot.com/bug?extid=8fdf0d8e10bdde1c2e88
>> Closes:
>https://lore.kernel.org/all/69f5ec0c.050a0220.312cd3.0023.GAE@xxxxxxxxxx/T/

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

>> Cc: stable@xxxxxxxxxxxxxxx
>> Signed-off-by: Bradley Morgan <include@xxxxxxxxx>
>> ---
>>  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!