Messages in this thread | | | Date | Wed, 3 Aug 2022 16:58:59 +0800 | Subject | Re: [PATCH] sched/debug: avoid executing show_state and causing rcu stall warning | From | Liu Song <> |
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> * Liu Song <liusong@linux.alibaba.com> wrote: > >> From: Liu Song <liusong@linux.alibaba.com> >> >> If the number of CPUs is large, "sysrq_sched_debug_show" will execute for >> a long time. Every time I execute "echo t > /proc/sysrq-trigger" on my >> 128-core machine, the rcu stall warning will be triggered. Moreover, >> sysrq_sched_debug_show does not need to be protected by rcu_read_lock, > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ >> and no rcu stall warning will appear after adjustment. >> > That doesn't mean it doesn't have to be protected by *any* lock - which > your patch implements AFAICS. > > There's a couple of lines such as: > > for_each_online_cpu(cpu) {
Hi,
Here I refer to the implementation of "sysrq_timer_list_show", and I don't see any lock.
Maybe there is a problem with the implementation of "sysrq_timer_list_show".
Thanks
> > ... which need to be protected against CPU hotplug events. > > I haven't checked any of the deeper code to see what RCU or other > protection it may need, but clearly you didn't either ... > > Thanks, > > Ingo
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