Messages in this thread | | | Subject | Re: [PATCH] arm64/smp: Move rcu_cpu_starting() earlier | From | Qian Cai <> | Date | Thu, 05 Nov 2020 18:02:49 -0500 |
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On Thu, 2020-11-05 at 22:22 +0000, Will Deacon wrote: > On Fri, Oct 30, 2020 at 04:33:25PM +0000, Will Deacon wrote: > > On Wed, 28 Oct 2020 14:26:14 -0400, Qian Cai wrote: > > > The call to rcu_cpu_starting() in secondary_start_kernel() is not early > > > enough in the CPU-hotplug onlining process, which results in lockdep > > > splats as follows: > > > > > > WARNING: suspicious RCU usage > > > ----------------------------- > > > kernel/locking/lockdep.c:3497 RCU-list traversed in non-reader section!! > > > > > > [...] > > > > Applied to arm64 (for-next/fixes), thanks! > > > > [1/1] arm64/smp: Move rcu_cpu_starting() earlier > > https://git.kernel.org/arm64/c/ce3d31ad3cac > > Hmm, this patch has caused a regression in the case that we fail to > online a CPU because it has incompatible CPU features and so we park it > in cpu_die_early(). We now get an endless spew of RCU stalls because the > core will never come online, but is being tracked by RCU. So I'm tempted > to revert this and live with the lockdep warning while we figure out a > proper fix. > > What's the correct say to undo rcu_cpu_starting(), given that we cannot > invoke the full hotplug machinery here? Is it correct to call > rcutree_dying_cpu() on the bad CPU and then rcutree_dead_cpu() from the > CPU doing cpu_up(), or should we do something else? It looks to me that rcu_report_dead() does the opposite of rcu_cpu_starting(), so lift rcu_report_dead() out of CONFIG_HOTPLUG_CPU and use it there to rewind, Paul?
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