Re: [PATCH 2/2] arm64: smp: Tell RCU about CPUs that fail to come online
From: "Paul E. McKenney" <paulmck@kernel.org>
Date: 2020-11-06 14:43:16
Also in:
lkml
On Fri, Nov 06, 2020 at 10:36:02AM +0000, Will Deacon wrote:
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 <redacted>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Suggested-by: Qian Cai <redacted>
Signed-off-by: Will Deacon <will@kernel.org>Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
quoted hunk ↗ jump to hunk
--- 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 09c96f57818c..18e9727d3f64 100644 --- a/arch/arm64/kernel/smp.c +++ b/arch/arm64/kernel/smp.c@@ -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);diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 2a52f42f64b6..bd04b09b84b3 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c@@ -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-- 2.29.1.341.ge80a0c044ae-goog
_______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel