Hi Daniel,
On Tue, May 8, 2018 at 9:23 AM, Daniel Wagner <wagi@xxxxxxxxx> wrote:
> On 05/07/2018 02:47 PM, Sebastian Andrzej Siewior wrote:
>> On 2018-05-03 09:43:33 [+0200], Geert Uytterhoeven wrote:
>>>> --- a/drivers/tty/serial/sh-sci.c
>>>> +++ b/drivers/tty/serial/sh-sci.c
>>>> @@ -2516,13 +2516,12 @@ static void serial_console_write(struct console
>>>> *co, const char *s,
>>>> unsigned long flags;
>>>> int locked = 1;
>>>>
>>>> - local_irq_save(flags);
>>>
>>>
>>> Hence the below now runs with local interrupts enabled.
>>>
>>> For checking port->sysrq or oops_in_progress that probably isn't an
>>> issue.
>>> If oops_in_progress is set, you have other problems, and the race
>>> condition
>>> between checking the flag and calling spin_lock{,_irqsave}() existed
>>> before,
>>> and is hard to avoid.
>>
>> while oops_in_progress is an issue of its own, the port->sysrq isn't
>> avoided by by local_irq_save(). On SMP systems you can still receive a
>> `break' signal on the UART and have a `printk()' issued on another CPU.
>>
>>> For actual console printing, I think you want to keep interrupts
>>> disabled.
>>
>> why? They should be disabled as part of getting the lock and not for any
>> other reason.
>>
>>>> if (port->sysrq)
>>>> locked = 0;
>>>> else if (oops_in_progress)
>>>> - locked = spin_trylock(&port->lock);
>>>> + locked = spin_trylock_irqsave(&port->lock, flags);
>>>> else
>>>> - spin_lock(&port->lock);
>>>> + spin_lock_irqsave(&port->lock, flags);
>>>
>>>
>>> Add
>>>
>>> if (!locked
>>> local_irq_save(flags)
>>>
>>> here?
>>
>>
>> So for oops_in_progress you get here with interrupts disabled. And if
>> not, I don't see the point in disabling the interrupts without any kind
>> of locking.
>
>
> So I understand, the initial version of this patch was correct.
>
> @Geert if you don't object I'll send a v3 (v1 ported to mainline).
Please go ahead, thanks!
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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