Re: [PATCH] iommu: Avoid softlockup and rcu stall in fq_flush_timeout().

[Peng Zhang]

在 2023/2/16 16:49, Hillf Danton 写道:
> On Thu, 16 Feb 2023 15:11:48 +0800 Peng Zhang <zhangpeng.00@xxxxxxxxxxxxx>
> > There is softlockup under fio pressure test with smmu enabled:
> > watchdog: BUG: soft lockup - CPU#81 stuck for 22s!  [swapper/81:0]
>
> What is your kernel version?
Rcu stall occurs in kernel version 5.4.
The test where the softlockup happened was not done by me, so I don't 
know the kernel version.
However, it is the same as the code logic of fq_flush_timeout in the 
mainline kernel.

> > This is because the timer callback fq_flush_timeout may run more than
> > 10ms, and timer may be processed continuously in the softirq so trigger
> > softlockup and rcu stall. We can use work to deal with fq_ring_free for
> > each cpu which may take long time, that to avoid triggering softlockup
> > and rcu stall.
> >
> > This patch is modified from the patch[1] of openEuler.
>
> Because of a timer hog observed on your system with 128 CPUs for instance
> does it make any sense to ask Peter to apply the patch for his 2-CPU box?
What is 2-CPU box?