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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 <quic_neeraju@quicinc.com>
Signed-off-by: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2022-01-24 15:41:32 -08:00
parent 2ec303113d
commit e2f638365d
1 changed files with 13 additions and 0 deletions
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13
kernel/rcu/srcutree.c
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@ -562,6 +562,7 @@ static void srcu_gp_end(struct srcu_struct *ssp)
unsigned long mask; unsigned long mask;
struct srcu_data *sdp; struct srcu_data *sdp;
struct srcu_node *snp; struct srcu_node *snp;
int ss_state;
/* Prevent more than one additional grace period. */ /* Prevent more than one additional grace period. */
mutex_lock(&ssp->srcu_cb_mutex); mutex_lock(&ssp->srcu_cb_mutex);
@ -629,6 +630,15 @@ static void srcu_gp_end(struct srcu_struct *ssp)
} else { } else {
spin_unlock_irq_rcu_node(ssp); 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) void srcu_barrier(struct srcu_struct *ssp)
{ {
int cpu; int cpu;
int idx;
unsigned long s = rcu_seq_snap(&ssp->srcu_barrier_seq); unsigned long s = rcu_seq_snap(&ssp->srcu_barrier_seq);
check_init_srcu_struct(ssp); 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. */ /* Initial count prevents reaching zero until all CBs are posted. */
atomic_set(&ssp->srcu_barrier_cpu_cnt, 1); 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) if (smp_load_acquire(&ssp->srcu_size_state) < SRCU_SIZE_WAIT_BARRIER)
srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda, 0)); srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda, 0));
else else
for_each_possible_cpu(cpu) for_each_possible_cpu(cpu)
srcu_barrier_one_cpu(ssp, per_cpu_ptr(ssp->sda, 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. */ /* Remove the initial count, at which point reaching zero can happen. */
if (atomic_dec_and_test(&ssp->srcu_barrier_cpu_cnt)) if (atomic_dec_and_test(&ssp->srcu_barrier_cpu_cnt))