From 0742ac3e2f9f4b8a3a394a270d8685078837662b Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Tue, 11 Oct 2016 06:09:59 -0700 Subject: [PATCH] rcu: Make expedited grace periods recheck dyntick idle state Expedited grace periods check dyntick-idle state, and avoid sending IPIs to idle CPUs, including those running guest OSes, and, on NOHZ_FULL kernels, nohz_full CPUs. However, the kernel has been observed checking a CPU while it was non-idle, but sending the IPI after it has gone idle. This commit therefore rechecks idle state immediately before sending the IPI, refraining from IPIing CPUs that have since gone idle. Reported-by: Rik van Riel Signed-off-by: Paul E. McKenney --- kernel/rcu/tree.h | 1 + kernel/rcu/tree_exp.h | 12 +++++++++++- 2 files changed, 12 insertions(+), 1 deletion(-) diff --git a/kernel/rcu/tree.h b/kernel/rcu/tree.h index e99a5234d9ed..fe98dd24adf8 100644 --- a/kernel/rcu/tree.h +++ b/kernel/rcu/tree.h @@ -404,6 +404,7 @@ struct rcu_data { atomic_long_t exp_workdone1; /* # done by others #1. */ atomic_long_t exp_workdone2; /* # done by others #2. */ atomic_long_t exp_workdone3; /* # done by others #3. */ + int exp_dynticks_snap; /* Double-check need for IPI. */ /* 7) Callback offloading. */ #ifdef CONFIG_RCU_NOCB_CPU diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index 24343eb87b58..d3053e99fdb6 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -358,8 +358,10 @@ static void sync_rcu_exp_select_cpus(struct rcu_state *rsp, 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); if (raw_smp_processor_id() == cpu || - !(atomic_add_return(0, &rdtp->dynticks) & 0x1) || + !(rdp->exp_dynticks_snap & 0x1) || !(rnp->qsmaskinitnext & rdp->grpmask)) mask_ofl_test |= rdp->grpmask; } @@ -377,9 +379,17 @@ static void sync_rcu_exp_select_cpus(struct rcu_state *rsp, /* IPI the remaining CPUs for expedited quiescent state. */ 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) != + rdp->exp_dynticks_snap) { + mask_ofl_test |= mask; + continue; + } ret = smp_call_function_single(cpu, func, rsp, 0); if (!ret) { mask_ofl_ipi &= ~mask; -- 2.39.5