From 8b2f63ab05eb233b2b396e133889ce3d1d30d944 Mon Sep 17 00:00:00 2001 From: Paul E. McKenney Date: Wed, 2 Nov 2016 14:12:05 -0700 Subject: rcu: Abstract the dynticks snapshot operation This commit is the second step towards full abstraction of all accesses to the ->dynticks counter, implementing the previously open-coded atomic add of zero in a new rcu_dynticks_snap() function. This abstraction will ease changes o the ->dynticks counter operation. Signed-off-by: Paul E. McKenney Reviewed-by: Josh Triplett --- kernel/rcu/tree.c | 19 ++++++++++++++++--- kernel/rcu/tree_exp.h | 6 ++---- 2 files changed, 18 insertions(+), 7 deletions(-) diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c index 14e283c351f6..805d55ee0b2a 100644 --- a/kernel/rcu/tree.c +++ b/kernel/rcu/tree.c @@ -281,6 +281,17 @@ static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = { #endif /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */ }; +/* + * 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_dynticks *rdtp) +{ + int snap = atomic_add_return(0, &rdtp->dynticks); + + return snap; +} + /* * Do a double-increment of the ->dynticks counter to emulate a * momentary idle-CPU quiescent state. @@ -1049,7 +1060,9 @@ void rcu_nmi_exit(void) */ bool notrace __rcu_is_watching(void) { - return atomic_read(this_cpu_ptr(&rcu_dynticks.dynticks)) & 0x1; + struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks); + + return atomic_read(&rdtp->dynticks) & 0x1; } /** @@ -1132,7 +1145,7 @@ static int rcu_is_cpu_rrupt_from_idle(void) static int dyntick_save_progress_counter(struct rcu_data *rdp, bool *isidle, unsigned long *maxj) { - rdp->dynticks_snap = atomic_add_return(0, &rdp->dynticks->dynticks); + rdp->dynticks_snap = rcu_dynticks_snap(rdp->dynticks); rcu_sysidle_check_cpu(rdp, isidle, maxj); if ((rdp->dynticks_snap & 0x1) == 0) { trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti")); @@ -1157,7 +1170,7 @@ static int rcu_implicit_dynticks_qs(struct rcu_data *rdp, int *rcrmp; unsigned int snap; - curr = (unsigned int)atomic_add_return(0, &rdp->dynticks->dynticks); + curr = (unsigned int)rcu_dynticks_snap(rdp->dynticks); snap = (unsigned int)rdp->dynticks_snap; /* diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index e59e1849b89a..011f626b2fd8 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -356,10 +356,9 @@ static void sync_rcu_exp_select_cpus(struct rcu_state *rsp, mask_ofl_test = 0; for_each_leaf_node_possible_cpu(rnp, cpu) { struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); - struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); rdp->exp_dynticks_snap = - atomic_add_return(0, &rdtp->dynticks); + rcu_dynticks_snap(rdp->dynticks); if (raw_smp_processor_id() == cpu || !(rdp->exp_dynticks_snap & 0x1) || !(rnp->qsmaskinitnext & rdp->grpmask)) @@ -380,12 +379,11 @@ static void sync_rcu_exp_select_cpus(struct rcu_state *rsp, for_each_leaf_node_possible_cpu(rnp, cpu) { unsigned long mask = leaf_node_cpu_bit(rnp, cpu); struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu); - struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu); if (!(mask_ofl_ipi & mask)) continue; retry_ipi: - if (atomic_add_return(0, &rdtp->dynticks) != + if (rcu_dynticks_snap(rdp->dynticks) != rdp->exp_dynticks_snap) { mask_ofl_test |= mask; continue; -- cgit v1.2.3-55-g7522