| Message ID | 20201106103602.9849-3-will@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | arm64: Fix issues with CPU hotplug and RCU | expand |
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 <cai@redhat.com> > Cc: "Paul E. McKenney" <paulmck@kernel.org> > Suggested-by: Qian Cai <cai@redhat.com> > Signed-off-by: Will Deacon <will@kernel.org> Reviewed-by: Paul E. McKenney <paulmck@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 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 >
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
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> Suggested-by: Qian Cai <cai@redhat.com> Signed-off-by: Will Deacon <will@kernel.org> --- arch/arm64/kernel/smp.c | 1 + kernel/rcu/tree.c | 2 +- 2 files changed, 2 insertions(+), 1 deletion(-)