Commit 04e613de authored Nov 06, 2020 by Will Deacon

arm64: smp: Tell RCU about CPUs that fail to come online



Commit ce3d31ad ("arm64/smp: Move rcu_cpu_starting() earlier") ensured
that RCU is informed early about incoming CPUs that might end up calling
into printk() before they are online. However, if such a CPU fails the
early CPU feature compatibility checks in check_local_cpu_capabilities(),
then it will be powered off or parked without informing RCU, leading to
an endless stream of stalls:

  | rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
  | rcu:	2-O...: (0 ticks this GP) idle=002/1/0x4000000000000000 softirq=0/0 fqs=2593
  | (detected by 0, t=5252 jiffies, g=9317, q=136)
  | Task dump for CPU 2:
  | task:swapper/2       state:R  running task     stack:    0 pid:    0 ppid:     1 flags:0x00000028
  | Call trace:
  | ret_from_fork+0x0/0x30

Ensure that the dying CPU invokes rcu_report_dead() prior to being powered
off or parked.

Cc: Qian Cai <cai@redhat.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Suggested-by: Qian Cai <cai@redhat.com>
Link: https://lore.kernel.org/r/20201105222242.GA8842@willie-the-truck
Link: https://lore.kernel.org/r/20201106103602.9849-3-will@kernel.org


Signed-off-by: Will Deacon <will@kernel.org>

parent 891deb87

arch/arm64/kernel/smp.c

+1 −0

Original line number	Diff line number	Diff line
		@@ -413,6 +413,7 @@ void cpu_die_early(void)

		/* Mark this CPU absent */
		set_cpu_present(cpu, 0);
		rcu_report_dead(cpu);

		if (IS_ENABLED(CONFIG_HOTPLUG_CPU)) {
		update_cpu_boot_status(CPU_KILL_ME);

kernel/rcu/tree.c

+1 −1

Original line number	Diff line number	Diff line
		@@ -4077,7 +4077,6 @@ void rcu_cpu_starting(unsigned int cpu)
		smp_mb(); /* Ensure RCU read-side usage follows above initialization. */
		}

		#ifdef CONFIG_HOTPLUG_CPU
		/*
		* The outgoing function has no further need of RCU, so remove it from
		* the rcu_node tree's ->qsmaskinitnext bit masks.
		@@ -4117,6 +4116,7 @@ void rcu_report_dead(unsigned int cpu)
		rdp->cpu_started = false;
		}

		#ifdef CONFIG_HOTPLUG_CPU
		/*
		* The outgoing CPU has just passed through the dying-idle state, and we
		* are being invoked from the CPU that was IPIed to continue the offline

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