> OK, thanks. This looks slightly different from the Loongson problem: > > - In Loongson, we don't get stuck in RCU, but in > cpufreq_dbs_governor_stop -> irq_work_sync(). > > - I run non-preemptible kernel, and my system still gets stuck. > > What is common is that it's UP with i8259 PIC. > > A.
Now it's an interesting case. Because on my machine, the problem I encountered seems to be the identical one of the original thread, disabling preempting can effectively solve the lockup. Also, my issue is not only occuring on 4.20-rc1, but also on earlier kernels, with a lower probability. But on your machine, you have another non-identical, but closely- related issue. It seems the timing-dependent lockup of i8259 PIC can be triggered in different ways. The conclusion is clear though, there's a real lockup condition in i8259 PIC driver, and it's causing real issues. Aaro, have you tried submitting your i8259 patch to the mainline? Despite your concerns about its underlying cause, I think a fix should be submitted. If there are no objections from the maintainers, I suggest submitting it to the mainline upstream, and send it to linux-stable, requesting it to be applied on 3.16, 4.4, 4.9, 4.14, 4.19, 4.20 stable branches. If you are busy, I can help submitting. Tom Li
