From e2f638365dd6283b7df1cb5e82f5b2746359f062 Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Mon, 24 Jan 2022 15:41:32 -0800 Subject: srcu: Add size-state transitioning code This is just dead code at the moment, and will be used once the state-transition code is activated. Because srcu_barrier() must be aware of transition before call_srcu(), the state machine waits for an SRCU grace period before callbacks are queued to the non-CPU-0 queues. This requres that portions of srcu_barrier() be enclosed in an SRCU read-side critical section. Co-developed-by: Neeraj Upadhyay Signed-off-by: Neeraj Upadhyay Signed-off-by: Paul E. McKenney --- kernel/rcu/srcutree.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) (limited to 'kernel/rcu') diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c index e98cc218e42b..00f9aed6f7b9 100644 --- a/kernel/rcu/srcutree.c +++ b/kernel/rcu/srcutree.c @@ -562,6 +562,7 @@ static void srcu_gp_end(struct srcu_struct *ssp) unsigned long mask; struct srcu_data *sdp; struct srcu_node *snp; + int ss_state; /* Prevent more than one additional grace period. */ mutex_lock(&ssp->srcu_cb_mutex); @@ -629,6 +630,15 @@ static void srcu_gp_end(struct srcu_struct *ssp) } else { spin_unlock_irq_rcu_node(ssp); } + + /* Transition to big if needed. */ + ss_state = smp_load_acquire(&ssp->srcu_size_state); + if (ss_state != SRCU_SIZE_SMALL && ss_state != SRCU_SIZE_BIG) { + if (ss_state == SRCU_SIZE_ALLOC) + init_srcu_struct_nodes(ssp); + else + smp_store_release(&ssp->srcu_size_state, ss_state + 1); + } } /* @@ -1178,6 +1188,7 @@ static void srcu_barrier_one_cpu(struct srcu_struct *ssp, struct srcu_data *sdp) void srcu_barrier(struct srcu_struct *ssp) { int cpu; + int idx; unsigned long s = rcu_seq_snap(&ssp->srcu_barrier_seq); check_init_srcu_struct(ssp); @@ -1193,11 +1204,13 @@ void srcu_barrier(struct srcu_struct *ssp) /* Initial count prevents reaching zero until all CBs are posted. */ atomic_set(&ssp->srcu_barrier_cpu_cnt, 1); + idx = srcu_read_lock(ssp); if (smp_load_acquire(&ssp->srcu_size_state) < SRCU_SIZE_WAIT_BARRIER) srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda, 0)); else for_each_possible_cpu(cpu) srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda, cpu)); + srcu_read_unlock(ssp, idx); /* Remove the initial count, at which point reaching zero can happen. */ if (atomic_dec_and_test(&ssp->srcu_barrier_cpu_cnt)) -- cgit v1.2.3-70-g09d2