From: Will Deacon will@kernel.org
[ Upstream commit 04e613ded8c26489b3e0f9101b44462f780d1a35 ]
Commit ce3d31ad3cac ("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 Signed-off-by: Sasha Levin sashal@kernel.org --- arch/arm64/kernel/smp.c | 1 + kernel/rcu/tree.c | 2 +- 2 files changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c index 98c059b6bacae..361cfc55cf5a7 100644 --- a/arch/arm64/kernel/smp.c +++ b/arch/arm64/kernel/smp.c @@ -401,6 +401,7 @@ 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); diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index c8f62e2d02761..b4924fefe2745 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -4024,7 +4024,6 @@ 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. @@ -4064,6 +4063,7 @@ void rcu_report_dead(unsigned int cpu) per_cpu(rcu_cpu_started, cpu) = 0; }
+#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