On 2023/06/21 23:34, Sebastian Andrzej Siewior wrote:
>> Also, if local_irq_save() is hidden due to RT, what guarantees that
>>
>> write_seqlock_irqsave(&zonelist_update_seq, flags);
>> <<IRQ>>
>> some_timer_function() {
>> printk();
>> }
>> <<IRQ>>
>> printk_deferred_enter();
>>
>> does not happen because write_seqlock_irqsave() does not disable IRQ?
>
> I don't see how zonelist_update_seq and printk here are connected
> without the port lock/ or memory allocation. But there are two things
> that are different on RT which probably answer your question:
It is explained as the first deadlock scenario in commit 1007843a9190
("mm/page_alloc: fix potential deadlock on zonelist_update_seq seqlock").
We have to disable IRQ before making zonelist_update_seq.seqcount odd.
