Re: [PATCH 11/19] rcu/context_tracking: Move dynticks_nesting to context tracking

From: Paul E. McKenney
Date: Thu Mar 10 2022 - 15:01:30 EST

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On Wed, Mar 02, 2022 at 04:48:02PM +0100, Frederic Weisbecker wrote:
> The RCU eqs tracking is going to be performed by the context tracking
> subsystem. The related nesting counters thus need to be moved to the
> context tracking structure.
>
> Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>

Acked-by: Paul E. McKenney <paulmck@xxxxxxxxxx>

> Cc: Paul E. McKenney <paulmck@xxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Neeraj Upadhyay <quic_neeraju@xxxxxxxxxxx>
> Cc: Uladzislau Rezki <uladzislau.rezki@xxxxxxxx>
> Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
> Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
> Cc: Nicolas Saenz Julienne <nsaenz@xxxxxxxxxx>
> Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
> Cc: Xiongfeng Wang <wangxiongfeng2@xxxxxxxxxx>
> Cc: Yu Liao<liaoyu15@xxxxxxxxxx>
> Cc: Phil Auld <pauld@xxxxxxxxxx>
> Cc: Paul Gortmaker<paul.gortmaker@xxxxxxxxxxxxx>
> Cc: Alex Belits <abelits@xxxxxxxxxxx>
> ---
> include/linux/context_tracking_state.h | 1 +
> kernel/context_tracking.c | 1 +
> kernel/rcu/tree.c | 31 +++++++++++++-------------
> kernel/rcu/tree.h | 1 -
> kernel/rcu/tree_stall.h | 3 ++-
> 5 files changed, 20 insertions(+), 17 deletions(-)
>
> diff --git a/include/linux/context_tracking_state.h b/include/linux/context_tracking_state.h
> index 5ad0e481c5a3..bcb942945265 100644
> --- a/include/linux/context_tracking_state.h
> +++ b/include/linux/context_tracking_state.h
> @@ -24,6 +24,7 @@ struct context_tracking {
> } state;
> #endif
> atomic_t dynticks; /* Even value for idle, else odd. */
> + long dynticks_nesting; /* Track process nesting level. */
> };
>
> #ifdef CONFIG_CONTEXT_TRACKING
> diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
> index 77b61a7c9890..09a77884a4e3 100644
> --- a/kernel/context_tracking.c
> +++ b/kernel/context_tracking.c
> @@ -234,6 +234,7 @@ void __init context_tracking_init(void)
> #endif /* #ifdef CONFIG_CONTEXT_TRACKING_USER */
>
> DEFINE_PER_CPU(struct context_tracking, context_tracking) = {
> + .dynticks_nesting = 1,
> .dynticks = ATOMIC_INIT(1),
> };
> EXPORT_SYMBOL_GPL(context_tracking);
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 96eb8503f28e..8708d1a99565 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -75,7 +75,6 @@
> /* Data structures. */
>
> static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, rcu_data) = {
> - .dynticks_nesting = 1,
> .dynticks_nmi_nesting = DYNTICK_IRQ_NONIDLE,
> #ifdef CONFIG_RCU_NOCB_CPU
> .cblist.flags = SEGCBLIST_RCU_CORE,
> @@ -441,7 +440,7 @@ static int rcu_is_cpu_rrupt_from_idle(void)
> lockdep_assert_irqs_disabled();
>
> /* Check for counter underflows */
> - RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nesting) < 0,
> + RCU_LOCKDEP_WARN(__this_cpu_read(context_tracking.dynticks_nesting) < 0,
> "RCU dynticks_nesting counter underflow!");
> RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nmi_nesting) <= 0,
> "RCU dynticks_nmi_nesting counter underflow/zero!");
> @@ -457,7 +456,7 @@ static int rcu_is_cpu_rrupt_from_idle(void)
> WARN_ON_ONCE(!nesting && !is_idle_task(current));
>
> /* Does CPU appear to be idle from an RCU standpoint? */
> - return __this_cpu_read(rcu_data.dynticks_nesting) == 0;
> + return __this_cpu_read(context_tracking.dynticks_nesting) == 0;
> }
>
> #define DEFAULT_RCU_BLIMIT (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ? 1000 : 10)
> @@ -624,16 +623,16 @@ static noinstr void rcu_eqs_enter(bool user)
> WARN_ON_ONCE(rdp->dynticks_nmi_nesting != DYNTICK_IRQ_NONIDLE);
> WRITE_ONCE(rdp->dynticks_nmi_nesting, 0);
> WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
> - rdp->dynticks_nesting == 0);
> - if (rdp->dynticks_nesting != 1) {
> + ct->dynticks_nesting == 0);
> + if (ct->dynticks_nesting != 1) {
> // RCU will still be watching, so just do accounting and leave.
> - rdp->dynticks_nesting--;
> + ct->dynticks_nesting--;
> return;
> }
>
> lockdep_assert_irqs_disabled();
> instrumentation_begin();
> - trace_rcu_dyntick(TPS("Start"), rdp->dynticks_nesting, 0, atomic_read(&ct->dynticks));
> + trace_rcu_dyntick(TPS("Start"), ct->dynticks_nesting, 0, atomic_read(&ct->dynticks));
> WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
> rcu_preempt_deferred_qs(current);
>
> @@ -641,7 +640,7 @@ static noinstr void rcu_eqs_enter(bool user)
> instrument_atomic_write(&ct->dynticks, sizeof(ct->dynticks));
>
> instrumentation_end();
> - WRITE_ONCE(rdp->dynticks_nesting, 0); /* Avoid irq-access tearing. */
> + WRITE_ONCE(ct->dynticks_nesting, 0); /* Avoid irq-access tearing. */
> // RCU is watching here ...
> rcu_dynticks_eqs_enter();
> // ... but is no longer watching here.
> @@ -798,7 +797,7 @@ void rcu_irq_exit_check_preempt(void)
> {
> lockdep_assert_irqs_disabled();
>
> - RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nesting) <= 0,
> + RCU_LOCKDEP_WARN(__this_cpu_read(context_tracking.dynticks_nesting) <= 0,
> "RCU dynticks_nesting counter underflow/zero!");
> RCU_LOCKDEP_WARN(__this_cpu_read(rcu_data.dynticks_nmi_nesting) !=
> DYNTICK_IRQ_NONIDLE,
> @@ -824,11 +823,11 @@ static void noinstr rcu_eqs_exit(bool user)
>
> lockdep_assert_irqs_disabled();
> rdp = this_cpu_ptr(&rcu_data);
> - oldval = rdp->dynticks_nesting;
> + oldval = ct->dynticks_nesting;
> WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0);
> if (oldval) {
> // RCU was already watching, so just do accounting and leave.
> - rdp->dynticks_nesting++;
> + ct->dynticks_nesting++;
> return;
> }
> rcu_dynticks_task_exit();
> @@ -840,9 +839,9 @@ static void noinstr rcu_eqs_exit(bool user)
> // instrumentation for the noinstr rcu_dynticks_eqs_exit()
> instrument_atomic_write(&ct->dynticks, sizeof(ct->dynticks));
>
> - trace_rcu_dyntick(TPS("End"), rdp->dynticks_nesting, 1, atomic_read(&ct->dynticks));
> + trace_rcu_dyntick(TPS("End"), ct->dynticks_nesting, 1, atomic_read(&ct->dynticks));
> WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
> - WRITE_ONCE(rdp->dynticks_nesting, 1);
> + WRITE_ONCE(ct->dynticks_nesting, 1);
> WARN_ON_ONCE(rdp->dynticks_nmi_nesting);
> WRITE_ONCE(rdp->dynticks_nmi_nesting, DYNTICK_IRQ_NONIDLE);
> instrumentation_end();
> @@ -4122,12 +4121,13 @@ static void rcu_init_new_rnp(struct rcu_node *rnp_leaf)
> static void __init
> rcu_boot_init_percpu_data(int cpu)
> {
> + struct context_tracking *ct = this_cpu_ptr(&context_tracking);
> struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
>
> /* Set up local state, ensuring consistent view of global state. */
> rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu);
> INIT_WORK(&rdp->strict_work, strict_work_handler);
> - WARN_ON_ONCE(rdp->dynticks_nesting != 1);
> + WARN_ON_ONCE(ct->dynticks_nesting != 1);
> WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(cpu)));
> rdp->barrier_seq_snap = rcu_state.barrier_sequence;
> rdp->rcu_ofl_gp_seq = rcu_state.gp_seq;
> @@ -4152,6 +4152,7 @@ rcu_boot_init_percpu_data(int cpu)
> int rcutree_prepare_cpu(unsigned int cpu)
> {
> unsigned long flags;
> + struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu);
> struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
> struct rcu_node *rnp = rcu_get_root();
>
> @@ -4160,7 +4161,7 @@ int rcutree_prepare_cpu(unsigned int cpu)
> rdp->qlen_last_fqs_check = 0;
> rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs);
> rdp->blimit = blimit;
> - rdp->dynticks_nesting = 1; /* CPU not up, no tearing. */
> + ct->dynticks_nesting = 1; /* CPU not up, no tearing. */
> raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
>
> /*
> diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
> index 15246a3f0734..8050bab08f39 100644
> --- a/kernel/rcu/tree.h
> +++ b/kernel/rcu/tree.h
> @@ -186,7 +186,6 @@ struct rcu_data {
>
> /* 3) dynticks interface. */
> int dynticks_snap; /* Per-GP tracking for dynticks. */
> - long dynticks_nesting; /* Track process nesting level. */
> long dynticks_nmi_nesting; /* Track irq/NMI nesting level. */
> bool rcu_need_heavy_qs; /* GP old, so heavy quiescent state! */
> bool rcu_urgent_qs; /* GP old need light quiescent state. */
> diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
> index 202129b1c7e4..30a5e0a8ddb3 100644
> --- a/kernel/rcu/tree_stall.h
> +++ b/kernel/rcu/tree_stall.h
> @@ -429,6 +429,7 @@ static void print_cpu_stall_info(int cpu)
> {
> unsigned long delta;
> bool falsepositive;
> + struct context_tracking *ct = this_cpu_ptr(&context_tracking);
> struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
> char *ticks_title;
> unsigned long ticks_value;
> @@ -459,7 +460,7 @@ static void print_cpu_stall_info(int cpu)
> "!."[!delta],
> ticks_value, ticks_title,
> rcu_dynticks_snap(cpu) & 0xfff,
> - rdp->dynticks_nesting, rdp->dynticks_nmi_nesting,
> + ct->dynticks_nesting, rdp->dynticks_nmi_nesting,
> rdp->softirq_snap, kstat_softirqs_cpu(RCU_SOFTIRQ, cpu),
> data_race(rcu_state.n_force_qs) - rcu_state.n_force_qs_gpstart,
> falsepositive ? " (false positive?)" : "");
> --
> 2.25.1
>

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