Re: [PATCH] arm64/smp: Move rcu_cpu_starting() earlier
From: Qian Cai <hidden>
Date: 2020-11-05 23:02:59
Also in:
lkml
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:quoted
On Wed, 28 Oct 2020 14:26:14 -0400, Qian Cai wrote:quoted
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/ce3d31ad3cacHmm, 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? _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel