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Date: Sat, 14 Jan 2017 00:54:42 -0800 From: "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> To: linux-kernel@...r.kernel.org Cc: mingo@...nel.org, jiangshanlai@...il.com, dipankar@...ibm.com, akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com, josh@...htriplett.org, tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org, dhowells@...hat.com, edumazet@...gle.com, dvhart@...ux.intel.com, fweisbec@...il.com, oleg@...hat.com, bobby.prani@...il.com, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> Subject: [PATCH tip/core/rcu 3/6] rcu: Abstract dynticks extended quiescent state enter/exit operations This commit is the third step towards full abstraction of all accesses to the ->dynticks counter, implementing the previously open-coded atomic add of 1 and entry checks in a new rcu_dynticks_eqs_enter() function, and the same but with exit checks in a new rcu_dynticks_eqs_exit() function. This abstraction will ease changes to the ->dynticks counter operation. Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com> --- kernel/rcu/tree.c | 92 +++++++++++++++++++++++++++++++++++++++---------------- 1 file changed, 66 insertions(+), 26 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 805d55ee0b2a..fc49e008963a 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -282,6 +282,65 @@ static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = { }; /* + * Record entry into an extended quiescent state. This is only to be + * called when not already in an extended quiescent state. + */ +static void rcu_dynticks_eqs_enter(void) +{ + struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); + + /* + * CPUs seeing atomic_inc() must see prior RCU read-side critical + * sections, and we also must force ordering with the next idle + * sojourn. + */ + smp_mb__before_atomic(); /* See above. */ + atomic_inc(&rdtp->dynticks); + smp_mb__after_atomic(); /* See above. */ + WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && + atomic_read(&rdtp->dynticks) & 0x1); +} + +/* + * Record exit from an extended quiescent state. This is only to be + * called from an extended quiescent state. + */ +static void rcu_dynticks_eqs_exit(void) +{ + struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); + + /* + * CPUs seeing atomic_inc() must see prior idle sojourns, + * and we also must force ordering with the next RCU read-side + * critical section. + */ + smp_mb__before_atomic(); /* See above. */ + atomic_inc(&rdtp->dynticks); + smp_mb__after_atomic(); /* See above. */ + WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && + !(atomic_read(&rdtp->dynticks) & 0x1)); +} + +/* + * Reset the current CPU's ->dynticks counter to indicate that the + * newly onlined CPU is no longer in an extended quiescent state. + * This will either leave the counter unchanged, or increment it + * to the next non-quiescent value. + * + * The non-atomic test/increment sequence works because the upper bits + * of the ->dynticks counter are manipulated only by the corresponding CPU, + * or when the corresponding CPU is offline. + */ +static void rcu_dynticks_eqs_online(void) +{ + struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); + + if (atomic_read(&rdtp->dynticks) & 0x1) + return; + atomic_add(0x1, &rdtp->dynticks); +} + +/* * Snapshot the ->dynticks counter with full ordering so as to allow * stable comparison of this counter with past and future snapshots. */ @@ -693,7 +752,7 @@ static void rcu_eqs_enter_common(long long oldval, bool user) { struct rcu_state *rsp; struct rcu_data *rdp; - struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); + struct rcu_dynticks __maybe_unused *rdtp = this_cpu_ptr(&rcu_dynticks); trace_rcu_dyntick(TPS("Start"), oldval, rdtp->dynticks_nesting); if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && @@ -712,12 +771,7 @@ static void rcu_eqs_enter_common(long long oldval, bool user) do_nocb_deferred_wakeup(rdp); } rcu_prepare_for_idle(); - /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */ - smp_mb__before_atomic(); /* See above. */ - atomic_inc(&rdtp->dynticks); - smp_mb__after_atomic(); /* Force ordering with next sojourn. */ - WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && - atomic_read(&rdtp->dynticks) & 0x1); + rcu_dynticks_eqs_enter(); rcu_dynticks_task_enter(); /* @@ -846,15 +900,10 @@ void rcu_irq_exit_irqson(void) */ static void rcu_eqs_exit_common(long long oldval, int user) { - struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); + struct rcu_dynticks __maybe_unused *rdtp = this_cpu_ptr(&rcu_dynticks); rcu_dynticks_task_exit(); - smp_mb__before_atomic(); /* Force ordering w/previous sojourn. */ - atomic_inc(&rdtp->dynticks); - /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */ - smp_mb__after_atomic(); /* See above. */ - WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && - !(atomic_read(&rdtp->dynticks) & 0x1)); + rcu_dynticks_eqs_exit(); rcu_cleanup_after_idle(); trace_rcu_dyntick(TPS("End"), oldval, rdtp->dynticks_nesting); if (IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && @@ -1001,11 +1050,7 @@ void rcu_nmi_enter(void) * period (observation due to Andy Lutomirski). */ if (!(atomic_read(&rdtp->dynticks) & 0x1)) { - smp_mb__before_atomic(); /* Force delay from prior write. */ - atomic_inc(&rdtp->dynticks); - /* atomic_inc() before later RCU read-side crit sects */ - smp_mb__after_atomic(); /* See above. */ - WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1)); + rcu_dynticks_eqs_exit(); incby = 1; } rdtp->dynticks_nmi_nesting += incby; @@ -1043,11 +1088,7 @@ void rcu_nmi_exit(void) /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */ rdtp->dynticks_nmi_nesting = 0; - /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */ - smp_mb__before_atomic(); /* See above. */ - atomic_inc(&rdtp->dynticks); - smp_mb__after_atomic(); /* Force delay to next write. */ - WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1); + rcu_dynticks_eqs_enter(); } /** @@ -3800,8 +3841,7 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp) init_callback_list(rdp); /* Re-enable callbacks on this CPU. */ rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE; rcu_sysidle_init_percpu_data(rdp->dynticks); - atomic_set(&rdp->dynticks->dynticks, - (atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1); + rcu_dynticks_eqs_online(); raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */ /* -- 2.5.2
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