Messages in this thread | | | Date | Wed, 3 Aug 2022 11:10:17 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] sched/debug: avoid executing show_state and causing rcu stall warning |
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* Liu Song <liusong@linux.alibaba.com> wrote:
> > > * 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".
But we are talking about sysrq_sched_debug_show(), which your patch tries to relax the RCU locking of.
Thanks,
Ingo
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