Re: [PATCH 10/19] rcu/context_tracking: Move dynticks counter to context tracking

From: Paul E. McKenney
Date: Thu Mar 10 2022 - 15:00:39 EST

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On Wed, Mar 02, 2022 at 04:48:01PM +0100, Frederic Weisbecker wrote:
> In order to prepare for merging RCU dynticks counter into the context
> tracking state, move the rcu_data's dynticks field to the context
> tracking structure. It will later be mixed within the context tracking
> state itself.
>
> Signed-off-by: Frederic Weisbecker <frederic@xxxxxxxxxx>

Assuming that the context_tracking_state.h definitions get everywhere
they need to go in all configurations:

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 | 10 ++++-
> kernel/context_tracking.c | 9 ++--
> kernel/rcu/tree.c | 59 ++++++++++++++------------
> kernel/rcu/tree.h | 1 -
> kernel/rcu/tree_exp.h | 2 +-
> kernel/rcu/tree_stall.h | 4 +-
> 6 files changed, 48 insertions(+), 37 deletions(-)
>
> diff --git a/include/linux/context_tracking_state.h b/include/linux/context_tracking_state.h
> index cdc692caa01d..5ad0e481c5a3 100644
> --- a/include/linux/context_tracking_state.h
> +++ b/include/linux/context_tracking_state.h
> @@ -7,6 +7,7 @@
> #include <linux/context_tracking_irq.h>
>
> struct context_tracking {
> +#ifdef CONFIG_CONTEXT_TRACKING_USER
> /*
> * When active is false, probes are unset in order
> * to minimize overhead: TIF flags are cleared
> @@ -21,11 +22,16 @@ struct context_tracking {
> CONTEXT_USER,
> CONTEXT_GUEST,
> } state;
> +#endif
> + atomic_t dynticks; /* Even value for idle, else odd. */
> };
>
> -#ifdef CONFIG_CONTEXT_TRACKING_USER
> -extern struct static_key_false context_tracking_key;
> +#ifdef CONFIG_CONTEXT_TRACKING
> DECLARE_PER_CPU(struct context_tracking, context_tracking);
> +#endif
> +
> +#ifdef CONFIG_CONTEXT_TRACKING_USER
> +extern struct static_key_false context_tracking_key;
>
> static __always_inline bool context_tracking_enabled(void)
> {
> diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
> index ea22eb04750f..77b61a7c9890 100644
> --- a/kernel/context_tracking.c
> +++ b/kernel/context_tracking.c
> @@ -30,9 +30,6 @@
> DEFINE_STATIC_KEY_FALSE(context_tracking_key);
> EXPORT_SYMBOL_GPL(context_tracking_key);
>
> -DEFINE_PER_CPU(struct context_tracking, context_tracking);
> -EXPORT_SYMBOL_GPL(context_tracking);
> -
> static noinstr bool context_tracking_recursion_enter(void)
> {
> int recursion;
> @@ -236,6 +233,12 @@ void __init context_tracking_init(void)
>
> #endif /* #ifdef CONFIG_CONTEXT_TRACKING_USER */
>
> +DEFINE_PER_CPU(struct context_tracking, context_tracking) = {
> + .dynticks = ATOMIC_INIT(1),
> +};
> +EXPORT_SYMBOL_GPL(context_tracking);
> +
> +
> void ct_idle_enter(void)
> {
> rcu_idle_enter();
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index cadf5f5a4700..96eb8503f28e 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -77,7 +77,6 @@
> static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, rcu_data) = {
> .dynticks_nesting = 1,
> .dynticks_nmi_nesting = DYNTICK_IRQ_NONIDLE,
> - .dynticks = ATOMIC_INIT(1),
> #ifdef CONFIG_RCU_NOCB_CPU
> .cblist.flags = SEGCBLIST_RCU_CORE,
> #endif
> @@ -268,7 +267,7 @@ void rcu_softirq_qs(void)
> */
> static noinline noinstr unsigned long rcu_dynticks_inc(int incby)
> {
> - return arch_atomic_add_return(incby, this_cpu_ptr(&rcu_data.dynticks));
> + return arch_atomic_add_return(incby, this_cpu_ptr(&context_tracking.dynticks));
> }
>
> /*
> @@ -324,9 +323,9 @@ static noinstr void rcu_dynticks_eqs_exit(void)
> */
> static void rcu_dynticks_eqs_online(void)
> {
> - struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
> + struct context_tracking *ct = this_cpu_ptr(&context_tracking);
>
> - if (atomic_read(&rdp->dynticks) & 0x1)
> + if (atomic_read(&ct->dynticks) & 0x1)
> return;
> rcu_dynticks_inc(1);
> }
> @@ -338,17 +337,19 @@ static void rcu_dynticks_eqs_online(void)
> */
> static __always_inline bool rcu_dynticks_curr_cpu_in_eqs(void)
> {
> - return !(arch_atomic_read(this_cpu_ptr(&rcu_data.dynticks)) & 0x1);
> + return !(arch_atomic_read(this_cpu_ptr(&context_tracking.dynticks)) & 0x1);
> }
>
> /*
> * Snapshot the ->dynticks counter with full ordering so as to allow
> * stable comparison of this counter with past and future snapshots.
> */
> -static int rcu_dynticks_snap(struct rcu_data *rdp)
> +static int rcu_dynticks_snap(int cpu)
> {
> + struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu);
> +
> smp_mb(); // Fundamental RCU ordering guarantee.
> - return atomic_read_acquire(&rdp->dynticks);
> + return atomic_read_acquire(&ct->dynticks);
> }
>
> /*
> @@ -363,9 +364,7 @@ static bool rcu_dynticks_in_eqs(int snap)
> /* Return true if the specified CPU is currently idle from an RCU viewpoint. */
> bool rcu_is_idle_cpu(int cpu)
> {
> - struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
> -
> - return rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp));
> + return rcu_dynticks_in_eqs(rcu_dynticks_snap(cpu));
> }
>
> /*
> @@ -375,7 +374,7 @@ bool rcu_is_idle_cpu(int cpu)
> */
> static bool rcu_dynticks_in_eqs_since(struct rcu_data *rdp, int snap)
> {
> - return snap != rcu_dynticks_snap(rdp);
> + return snap != rcu_dynticks_snap(rdp->cpu);
> }
>
> /*
> @@ -384,11 +383,11 @@ static bool rcu_dynticks_in_eqs_since(struct rcu_data *rdp, int snap)
> */
> bool rcu_dynticks_zero_in_eqs(int cpu, int *vp)
> {
> - struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
> + struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu);
> int snap;
>
> // If not quiescent, force back to earlier extended quiescent state.
> - snap = atomic_read(&rdp->dynticks) & ~0x1;
> + snap = atomic_read(&ct->dynticks) & ~0x1;
>
> smp_rmb(); // Order ->dynticks and *vp reads.
> if (READ_ONCE(*vp))
> @@ -396,7 +395,7 @@ bool rcu_dynticks_zero_in_eqs(int cpu, int *vp)
> smp_rmb(); // Order *vp read and ->dynticks re-read.
>
> // If still in the same extended quiescent state, we are good!
> - return snap == atomic_read(&rdp->dynticks);
> + return snap == atomic_read(&ct->dynticks);
> }
>
> /*
> @@ -620,6 +619,7 @@ EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);
> static noinstr void rcu_eqs_enter(bool user)
> {
> struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
> + struct context_tracking *ct = this_cpu_ptr(&context_tracking);
>
> WARN_ON_ONCE(rdp->dynticks_nmi_nesting != DYNTICK_IRQ_NONIDLE);
> WRITE_ONCE(rdp->dynticks_nmi_nesting, 0);
> @@ -633,12 +633,12 @@ static noinstr void rcu_eqs_enter(bool user)
>
> lockdep_assert_irqs_disabled();
> instrumentation_begin();
> - trace_rcu_dyntick(TPS("Start"), rdp->dynticks_nesting, 0, atomic_read(&rdp->dynticks));
> + trace_rcu_dyntick(TPS("Start"), rdp->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);
>
> // instrumentation for the noinstr rcu_dynticks_eqs_enter()
> - instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks));
> + instrument_atomic_write(&ct->dynticks, sizeof(ct->dynticks));
>
> instrumentation_end();
> WRITE_ONCE(rdp->dynticks_nesting, 0); /* Avoid irq-access tearing. */
> @@ -740,7 +740,7 @@ noinstr void rcu_user_enter(void)
> * rcu_nmi_exit - inform RCU of exit from NMI context
> *
> * If we are returning from the outermost NMI handler that interrupted an
> - * RCU-idle period, update rdp->dynticks and rdp->dynticks_nmi_nesting
> + * RCU-idle period, update ct->dynticks and rdp->dynticks_nmi_nesting
> * to let the RCU grace-period handling know that the CPU is back to
> * being RCU-idle.
> *
> @@ -749,6 +749,7 @@ noinstr void rcu_user_enter(void)
> */
> noinstr void rcu_nmi_exit(void)
> {
> + struct context_tracking *ct = this_cpu_ptr(&context_tracking);
> struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
>
> instrumentation_begin();
> @@ -766,7 +767,7 @@ noinstr void rcu_nmi_exit(void)
> */
> if (rdp->dynticks_nmi_nesting != 1) {
> trace_rcu_dyntick(TPS("--="), rdp->dynticks_nmi_nesting, rdp->dynticks_nmi_nesting - 2,
> - atomic_read(&rdp->dynticks));
> + atomic_read(&ct->dynticks));
> WRITE_ONCE(rdp->dynticks_nmi_nesting, /* No store tearing. */
> rdp->dynticks_nmi_nesting - 2);
> instrumentation_end();
> @@ -774,11 +775,11 @@ noinstr void rcu_nmi_exit(void)
> }
>
> /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
> - trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, atomic_read(&rdp->dynticks));
> + trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, atomic_read(&ct->dynticks));
> WRITE_ONCE(rdp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */
>
> // instrumentation for the noinstr rcu_dynticks_eqs_enter()
> - instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks));
> + instrument_atomic_write(&ct->dynticks, sizeof(ct->dynticks));
> instrumentation_end();
>
> // RCU is watching here ...
> @@ -817,6 +818,7 @@ void rcu_irq_exit_check_preempt(void)
> */
> static void noinstr rcu_eqs_exit(bool user)
> {
> + struct context_tracking *ct = this_cpu_ptr(&context_tracking);
> struct rcu_data *rdp;
> long oldval;
>
> @@ -836,9 +838,9 @@ static void noinstr rcu_eqs_exit(bool user)
> instrumentation_begin();
>
> // instrumentation for the noinstr rcu_dynticks_eqs_exit()
> - instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks));
> + instrument_atomic_write(&ct->dynticks, sizeof(ct->dynticks));
>
> - trace_rcu_dyntick(TPS("End"), rdp->dynticks_nesting, 1, atomic_read(&rdp->dynticks));
> + trace_rcu_dyntick(TPS("End"), rdp->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);
> WARN_ON_ONCE(rdp->dynticks_nmi_nesting);
> @@ -944,7 +946,7 @@ void __rcu_irq_enter_check_tick(void)
> /**
> * rcu_nmi_enter - inform RCU of entry to NMI context
> *
> - * If the CPU was idle from RCU's viewpoint, update rdp->dynticks and
> + * If the CPU was idle from RCU's viewpoint, update ct->dynticks and
> * rdp->dynticks_nmi_nesting to let the RCU grace-period handling know
> * that the CPU is active. This implementation permits nested NMIs, as
> * long as the nesting level does not overflow an int. (You will probably
> @@ -957,6 +959,7 @@ noinstr void rcu_nmi_enter(void)
> {
> long incby = 2;
> struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
> + struct context_tracking *ct = this_cpu_ptr(&context_tracking);
>
> /* Complain about underflow. */
> WARN_ON_ONCE(rdp->dynticks_nmi_nesting < 0);
> @@ -980,9 +983,9 @@ noinstr void rcu_nmi_enter(void)
>
> instrumentation_begin();
> // instrumentation for the noinstr rcu_dynticks_curr_cpu_in_eqs()
> - instrument_atomic_read(&rdp->dynticks, sizeof(rdp->dynticks));
> + instrument_atomic_read(&ct->dynticks, sizeof(ct->dynticks));
> // instrumentation for the noinstr rcu_dynticks_eqs_exit()
> - instrument_atomic_write(&rdp->dynticks, sizeof(rdp->dynticks));
> + instrument_atomic_write(&ct->dynticks, sizeof(ct->dynticks));
>
> incby = 1;
> } else if (!in_nmi()) {
> @@ -994,7 +997,7 @@ noinstr void rcu_nmi_enter(void)
>
> trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="),
> rdp->dynticks_nmi_nesting,
> - rdp->dynticks_nmi_nesting + incby, atomic_read(&rdp->dynticks));
> + rdp->dynticks_nmi_nesting + incby, atomic_read(&ct->dynticks));
> instrumentation_end();
> WRITE_ONCE(rdp->dynticks_nmi_nesting, /* Prevent store tearing. */
> rdp->dynticks_nmi_nesting + incby);
> @@ -1138,7 +1141,7 @@ static void rcu_gpnum_ovf(struct rcu_node *rnp, struct rcu_data *rdp)
> */
> static int dyntick_save_progress_counter(struct rcu_data *rdp)
> {
> - rdp->dynticks_snap = rcu_dynticks_snap(rdp);
> + rdp->dynticks_snap = rcu_dynticks_snap(rdp->cpu);
> if (rcu_dynticks_in_eqs(rdp->dynticks_snap)) {
> trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti"));
> rcu_gpnum_ovf(rdp->mynode, rdp);
> @@ -4125,7 +4128,7 @@ rcu_boot_init_percpu_data(int cpu)
> 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(rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp)));
> + 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;
> rdp->rcu_ofl_gp_flags = RCU_GP_CLEANED;
> diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h
> index b8d07bf92d29..15246a3f0734 100644
> --- a/kernel/rcu/tree.h
> +++ b/kernel/rcu/tree.h
> @@ -188,7 +188,6 @@ struct rcu_data {
> int dynticks_snap; /* Per-GP tracking for dynticks. */
> long dynticks_nesting; /* Track process nesting level. */
> long dynticks_nmi_nesting; /* Track irq/NMI nesting level. */
> - atomic_t dynticks; /* Even value for idle, else odd. */
> bool rcu_need_heavy_qs; /* GP old, so heavy quiescent state! */
> bool rcu_urgent_qs; /* GP old need light quiescent state. */
> bool rcu_forced_tick; /* Forced tick to provide QS. */
> diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
> index d5f30085b0cf..2210110990f4 100644
> --- a/kernel/rcu/tree_exp.h
> +++ b/kernel/rcu/tree_exp.h
> @@ -358,7 +358,7 @@ static void sync_rcu_exp_select_node_cpus(struct work_struct *wp)
> !(rnp->qsmaskinitnext & mask)) {
> mask_ofl_test |= mask;
> } else {
> - snap = rcu_dynticks_snap(rdp);
> + snap = rcu_dynticks_snap(cpu);
> if (rcu_dynticks_in_eqs(snap))
> mask_ofl_test |= mask;
> else
> diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h
> index 84b812a3ab44..202129b1c7e4 100644
> --- a/kernel/rcu/tree_stall.h
> +++ b/kernel/rcu/tree_stall.h
> @@ -448,7 +448,7 @@ static void print_cpu_stall_info(int cpu)
> }
> delta = rcu_seq_ctr(rdp->mynode->gp_seq - rdp->rcu_iw_gp_seq);
> falsepositive = rcu_is_gp_kthread_starving(NULL) &&
> - rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp));
> + rcu_dynticks_in_eqs(rcu_dynticks_snap(cpu));
> pr_err("\t%d-%c%c%c%c: (%lu %s) idle=%03x/%ld/%#lx softirq=%u/%u fqs=%ld %s\n",
> cpu,
> "O."[!!cpu_online(cpu)],
> @@ -458,7 +458,7 @@ static void print_cpu_stall_info(int cpu)
> rdp->rcu_iw_pending ? (int)min(delta, 9UL) + '0' :
> "!."[!delta],
> ticks_value, ticks_title,
> - rcu_dynticks_snap(rdp) & 0xfff,
> + rcu_dynticks_snap(cpu) & 0xfff,
> rdp->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,
> --
> 2.25.1
>

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