Re: [RESEND][patch V3 17/23] rcu/tree: Mark the idle relevant functions noinstr

From: Paul E. McKenney
Date: Tue Mar 24 2020 - 12:09:13 EST

Next message: Christian Brauner: "Re: clone3: allow creation of time namespace with offset"
Previous message: Jens Axboe: "Re: [PATCH v3 0/3] block/diskstats: more accurate io_ticks and optimization"
Next in thread: Thomas Gleixner: "Re: [RESEND][patch V3 17/23] rcu/tree: Mark the idle relevant functions noinstr"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

On Fri, Mar 20, 2020 at 07:00:13PM +0100, Thomas Gleixner wrote:
> These functions are invoked from context tracking and other places in the
> low level entry code. Move them into the .noinstr.text section to exclude
> them from instrumentation.
>
> Mark the places which are safe to invoke traceable functions with
> instr_begin/end() so objtool won't complain.
>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>

A few questions and comments below. I have not yet tried rcutorture
on this series, but this is on my list. (Just when you thought it
was safe...)

Thanx, Paul

> ---
> V3: New patch
> ---
> kernel/rcu/tree.c | 66 ++++++++++++++++++++++++++---------------------
> kernel/rcu/tree_plugin.h | 4 +-
> kernel/rcu/update.c | 7 ++--
> 3 files changed, 42 insertions(+), 35 deletions(-)
>
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -75,9 +75,6 @@
> */
> #define RCU_DYNTICK_CTRL_MASK 0x1
> #define RCU_DYNTICK_CTRL_CTR (RCU_DYNTICK_CTRL_MASK + 1)
> -#ifndef rcu_eqs_special_exit
> -#define rcu_eqs_special_exit() do { } while (0)
> -#endif

Note to self: Check to see if anyone is ever going to use
rcu_eqs_special_set() and thus the bottom bit of ->dynticks, and get
rid of both if not. The rcu_eqs_special_exit() was to be how this
bit was to be sensed by the user.

> static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, rcu_data) = {
> .dynticks_nesting = 1,
> @@ -228,7 +225,7 @@ void rcu_softirq_qs(void)
> * RCU is watching prior to the call to this function and is no longer
> * watching upon return.
> */
> -static void rcu_dynticks_eqs_enter(void)
> +static noinstr void rcu_dynticks_eqs_enter(void)
> {
> struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
> int seq;
> @@ -252,7 +249,7 @@ static void rcu_dynticks_eqs_enter(void)
> * called from an extended quiescent state, that is, RCU is not watching
> * prior to the call to this function and is watching upon return.
> */
> -static void rcu_dynticks_eqs_exit(void)
> +static noinstr void rcu_dynticks_eqs_exit(void)
> {
> struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
> int seq;
> @@ -269,8 +266,6 @@ static void rcu_dynticks_eqs_exit(void)
> if (seq & RCU_DYNTICK_CTRL_MASK) {
> atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdp->dynticks);
> smp_mb__after_atomic(); /* _exit after clearing mask. */
> - /* Prefer duplicate flushes to losing a flush. */
> - rcu_eqs_special_exit();
> }
> }
>
> @@ -298,7 +293,7 @@ static void rcu_dynticks_eqs_online(void
> *
> * No ordering, as we are sampling CPU-local information.
> */
> -static bool rcu_dynticks_curr_cpu_in_eqs(void)
> +static __always_inline bool rcu_dynticks_curr_cpu_in_eqs(void)
> {
> struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
>
> @@ -557,7 +552,7 @@ EXPORT_SYMBOL_GPL(rcutorture_get_gp_data
> * the possibility of usermode upcalls having messed up our count
> * of interrupt nesting level during the prior busy period.
> */
> -static void rcu_eqs_enter(bool user)
> +static noinstr void rcu_eqs_enter(bool user)
> {
> struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
>
> @@ -572,12 +567,14 @@ static void rcu_eqs_enter(bool user)
> }
>
> lockdep_assert_irqs_disabled();
> + instr_begin();
> trace_rcu_dyntick(TPS("Start"), rdp->dynticks_nesting, 0, atomic_read(&rdp->dynticks));
> WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
> rdp = this_cpu_ptr(&rcu_data);
> do_nocb_deferred_wakeup(rdp);
> rcu_prepare_for_idle();
> rcu_preempt_deferred_qs(current);
> + instr_end();
> WRITE_ONCE(rdp->dynticks_nesting, 0); /* Avoid irq-access tearing. */
> // RCU is watching here ...
> rcu_dynticks_eqs_enter();
> @@ -614,7 +611,7 @@ void rcu_idle_enter(void)
> * If you add or remove a call to rcu_user_enter(), be sure to test with
> * CONFIG_RCU_EQS_DEBUG=y.
> */
> -void rcu_user_enter(void)
> +noinstr void rcu_user_enter(void)
> {
> lockdep_assert_irqs_disabled();

Just out of curiosity -- this means that lockdep_assert_irqs_disabled()
must be noinstr, correct?

> rcu_eqs_enter(true);
> @@ -647,19 +644,23 @@ static __always_inline void rcu_nmi_exit
> * leave it in non-RCU-idle state.
> */
> if (rdp->dynticks_nmi_nesting != 1) {
> + instr_begin();
> trace_rcu_dyntick(TPS("--="), rdp->dynticks_nmi_nesting, rdp->dynticks_nmi_nesting - 2,
> atomic_read(&rdp->dynticks));
> WRITE_ONCE(rdp->dynticks_nmi_nesting, /* No store tearing. */
> rdp->dynticks_nmi_nesting - 2);
> + instr_end();
> return;
> }
>
> + instr_begin();

Indentation?

> /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
> trace_rcu_dyntick(TPS("Startirq"), rdp->dynticks_nmi_nesting, 0, atomic_read(&rdp->dynticks));
> WRITE_ONCE(rdp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */
>
> if (irq)
> rcu_prepare_for_idle();
> + instr_end();
>
> // RCU is watching here ...
> rcu_dynticks_eqs_enter();
> @@ -675,7 +676,7 @@ static __always_inline void rcu_nmi_exit
> * If you add or remove a call to rcu_nmi_exit(), be sure to test
> * with CONFIG_RCU_EQS_DEBUG=y.
> */
> -void rcu_nmi_exit(void)
> +void noinstr rcu_nmi_exit(void)
> {
> rcu_nmi_exit_common(false);
> }
> @@ -728,7 +729,7 @@ void rcu_irq_exit_irqson(void)
> * allow for the possibility of usermode upcalls messing up our count of
> * interrupt nesting level during the busy period that is just now starting.
> */
> -static void rcu_eqs_exit(bool user)
> +static void noinstr rcu_eqs_exit(bool user)
> {
> struct rcu_data *rdp;
> long oldval;
> @@ -746,12 +747,14 @@ static void rcu_eqs_exit(bool user)
> // RCU is not watching here ...
> rcu_dynticks_eqs_exit();
> // ... but is watching here.
> + instr_begin();
> rcu_cleanup_after_idle();
> trace_rcu_dyntick(TPS("End"), rdp->dynticks_nesting, 1, atomic_read(&rdp->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);
> WRITE_ONCE(rdp->dynticks_nmi_nesting, DYNTICK_IRQ_NONIDLE);
> + instr_end();
> }
>
> /**
> @@ -782,7 +785,7 @@ void rcu_idle_exit(void)
> * If you add or remove a call to rcu_user_exit(), be sure to test with
> * CONFIG_RCU_EQS_DEBUG=y.
> */
> -void rcu_user_exit(void)
> +void noinstr rcu_user_exit(void)
> {
> rcu_eqs_exit(1);
> }
> @@ -830,27 +833,33 @@ static __always_inline void rcu_nmi_ente
> rcu_cleanup_after_idle();
>
> incby = 1;
> - } else if (irq && tick_nohz_full_cpu(rdp->cpu) &&
> - rdp->dynticks_nmi_nesting == DYNTICK_IRQ_NONIDLE &&
> - READ_ONCE(rdp->rcu_urgent_qs) && !rdp->rcu_forced_tick) {
> + } else if (irq) {
> // We get here only if we had already exited the extended
> // quiescent state and this was an interrupt (not an NMI).
> // Therefore, (1) RCU is already watching and (2) The fact
> // that we are in an interrupt handler and that the rcu_node
> // lock is an irq-disabled lock prevents self-deadlock.
> // So we can safely recheck under the lock.

The above comment is a bit misleading in this location.

> - raw_spin_lock_rcu_node(rdp->mynode);
> - if (rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) {
> - // A nohz_full CPU is in the kernel and RCU
> - // needs a quiescent state. Turn on the tick!
> - rdp->rcu_forced_tick = true;
> - tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
> + instr_begin();
> + if (tick_nohz_full_cpu(rdp->cpu) &&
> + rdp->dynticks_nmi_nesting == DYNTICK_IRQ_NONIDLE &&
> + READ_ONCE(rdp->rcu_urgent_qs) && !rdp->rcu_forced_tick) {

So how about like this?

// We get here only if we had already exited
// the extended quiescent state and this was an
// interrupt (not an NMI). Therefore, (1) RCU is
// already watching and (2) The fact that we are in
// an interrupt handler and that the rcu_node lock
// is an irq-disabled lock prevents self-deadlock.
// So we can safely recheck under the lock.

> + raw_spin_lock_rcu_node(rdp->mynode);
> + if (rdp->rcu_urgent_qs && !rdp->rcu_forced_tick) {
> + // A nohz_full CPU is in the kernel and RCU
> + // needs a quiescent state. Turn on the tick!
> + rdp->rcu_forced_tick = true;
> + tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU);
> + }
> + raw_spin_unlock_rcu_node(rdp->mynode);
> }
> - raw_spin_unlock_rcu_node(rdp->mynode);
> + instr_end();
> }
> + instr_begin();
> trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="),
> rdp->dynticks_nmi_nesting,
> rdp->dynticks_nmi_nesting + incby, atomic_read(&rdp->dynticks));
> + instr_end();
> WRITE_ONCE(rdp->dynticks_nmi_nesting, /* Prevent store tearing. */
> rdp->dynticks_nmi_nesting + incby);
> barrier();
> @@ -859,11 +868,10 @@ static __always_inline void rcu_nmi_ente
> /**
> * rcu_nmi_enter - inform RCU of entry to NMI context
> */
> -void rcu_nmi_enter(void)
> +noinstr void rcu_nmi_enter(void)
> {
> rcu_nmi_enter_common(false);
> }
> -NOKPROBE_SYMBOL(rcu_nmi_enter);
>
> /**
> * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
> @@ -932,7 +940,7 @@ static void rcu_disable_urgency_upon_qs(
> * if the current CPU is not in its idle loop or is in an interrupt or
> * NMI handler, return true.
> */
> -bool notrace rcu_is_watching(void)
> +noinstr bool rcu_is_watching(void)
> {
> bool ret;
>
> @@ -976,7 +984,7 @@ void rcu_request_urgent_qs_task(struct t
> * RCU on an offline processor during initial boot, hence the check for
> * rcu_scheduler_fully_active.
> */
> -bool rcu_lockdep_current_cpu_online(void)
> +noinstr bool rcu_lockdep_current_cpu_online(void)
> {
> struct rcu_data *rdp;
> struct rcu_node *rnp;
> @@ -984,12 +992,12 @@ bool rcu_lockdep_current_cpu_online(void
>
> if (in_nmi() || !rcu_scheduler_fully_active)
> return true;
> - preempt_disable();
> + preempt_disable_notrace();
> rdp = this_cpu_ptr(&rcu_data);
> rnp = rdp->mynode;
> if (rdp->grpmask & rcu_rnp_online_cpus(rnp))
> ret = true;
> - preempt_enable();
> + preempt_enable_notrace();
> return ret;
> }
> EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
> --- a/kernel/rcu/tree_plugin.h
> +++ b/kernel/rcu/tree_plugin.h
> @@ -2546,7 +2546,7 @@ static void rcu_bind_gp_kthread(void)
> }
>
> /* Record the current task on dyntick-idle entry. */
> -static void rcu_dynticks_task_enter(void)
> +static void noinstr rcu_dynticks_task_enter(void)
> {
> #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
> WRITE_ONCE(current->rcu_tasks_idle_cpu, smp_processor_id());
> @@ -2554,7 +2554,7 @@ static void rcu_dynticks_task_enter(void
> }
>
> /* Record no current task on dyntick-idle exit. */
> -static void rcu_dynticks_task_exit(void)
> +static void noinstr rcu_dynticks_task_exit(void)
> {
> #if defined(CONFIG_TASKS_RCU) && defined(CONFIG_NO_HZ_FULL)
> WRITE_ONCE(current->rcu_tasks_idle_cpu, -1);
> --- a/kernel/rcu/update.c
> +++ b/kernel/rcu/update.c
> @@ -95,7 +95,7 @@ module_param(rcu_normal_after_boot, int,
> * Similarly, we avoid claiming an RCU read lock held if the current
> * CPU is offline.
> */
> -static bool rcu_read_lock_held_common(bool *ret)
> +static noinstr bool rcu_read_lock_held_common(bool *ret)
> {
> if (!debug_lockdep_rcu_enabled()) {
> *ret = 1;
> @@ -112,7 +112,7 @@ static bool rcu_read_lock_held_common(bo
> return false;
> }
>
> -int rcu_read_lock_sched_held(void)
> +noinstr int rcu_read_lock_sched_held(void)
> {
> bool ret;
>
> @@ -246,13 +246,12 @@ struct lockdep_map rcu_callback_map =
> STATIC_LOCKDEP_MAP_INIT("rcu_callback", &rcu_callback_key);
> EXPORT_SYMBOL_GPL(rcu_callback_map);
>
> -int notrace debug_lockdep_rcu_enabled(void)
> +noinstr int notrace debug_lockdep_rcu_enabled(void)
> {
> return rcu_scheduler_active != RCU_SCHEDULER_INACTIVE && debug_locks &&
> current->lockdep_recursion == 0;
> }
> EXPORT_SYMBOL_GPL(debug_lockdep_rcu_enabled);
> -NOKPROBE_SYMBOL(debug_lockdep_rcu_enabled);
>
> /**
> * rcu_read_lock_held() - might we be in RCU read-side critical section?
>

Next message: Christian Brauner: "Re: clone3: allow creation of time namespace with offset"
Previous message: Jens Axboe: "Re: [PATCH v3 0/3] block/diskstats: more accurate io_ticks and optimization"
Next in thread: Thomas Gleixner: "Re: [RESEND][patch V3 17/23] rcu/tree: Mark the idle relevant functions noinstr"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]