Re: [PATCH] net/skbuff: silence warnings under memory pressure

On (09/04/19 08:54), Michal Hocko wrote:

I am sorry, I could have been more explicit when CCing you.

Oh, sorry! My bad!

Sure the ratelimit is part of the problem. But I was more interested
in the potential livelock (infinite loop) mentioned by Qian Cai. It
is not important whether we generate one or more lines of output from
the softirq context as long as the printk generates more irq processing
which might end up doing the same. Is this really possible?

Hmm. I need to look at this more... wake_up_klogd() queues work only once
on particular CPU: irq_work_queue(this_cpu_ptr(&wake_up_klogd_work));

bool irq_work_queue()
{
	/* Only queue if not already pending */
	if (!irq_work_claim(work))
		return false;

	 __irq_work_queue_local(work);
}

softirqs are processed in batches, right? The softirq batch can add XXXX
lines to printk logbuf, but there will be only one PRINTK_PENDING_WAKEUP
queued. Qian Cai mentioned that "net_rx_action softirqs again which are
plenty due to connected via ssh etc." so the proportion still seems to be
N:1 - we process N softirqs, add 1 printk irq_work.

But need to think more.
Interesting question.

	-ss