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rcu: Make synchronize_rcu() fast path update ->gp_seq counters 

This commit causes the early boot single-CPU synchronize_rcu() fastpath to
update the rcu_state and rcu_node structures' ->gp_seq and ->gp_seq_needed
counters.  This will allow the full-state polled grace-period APIs to
detect all normal grace periods without the need to track the special
combined polling-only counter, which is a step towards removing the
->rgos_polled field from the rcu_gp_oldstate, thereby reducing its size
by one third.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2022-08-04 17:28:01 -07:00
parent 5f11bad6b7
commit 910e12092e
1 changed files with 26 additions and 13 deletions
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39
kernel/rcu/tree.c
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@ -3480,24 +3480,37 @@ static int rcu_blocking_is_gp(void)
*/
void synchronize_rcu(void)
{
unsigned long flags;
struct rcu_node *rnp;
RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
lock_is_held(&rcu_lock_map) ||
lock_is_held(&rcu_sched_lock_map),
"Illegal synchronize_rcu() in RCU read-side critical section");
if (rcu_blocking_is_gp()) {
// Note well that this code runs with !PREEMPT && !SMP.
// In addition, all code that advances grace periods runs at
// process level. Therefore, this normal GP overlaps with
// other normal GPs only by being fully nested within them,
// which allows reuse of ->gp_seq_polled_snap.
rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_snap);
rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_snap);
return; // Context allows vacuous grace periods.
if (!rcu_blocking_is_gp()) {
if (rcu_gp_is_expedited())
synchronize_rcu_expedited();
else
wait_rcu_gp(call_rcu);
return;
}
if (rcu_gp_is_expedited())
synchronize_rcu_expedited();
else
wait_rcu_gp(call_rcu);
// Context allows vacuous grace periods.
// Note well that this code runs with !PREEMPT && !SMP.
// In addition, all code that advances grace periods runs at
// process level. Therefore, this normal GP overlaps with other
// normal GPs only by being fully nested within them, which allows
// reuse of ->gp_seq_polled_snap.
rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_snap);
rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_snap);
// Update normal grace-period counters to record grace period.
local_irq_save(flags);
WARN_ON_ONCE(num_online_cpus() > 1);
rcu_state.gp_seq += (1 << RCU_SEQ_CTR_SHIFT);
rcu_for_each_node_breadth_first(rnp)
rnp->gp_seq_needed = rnp->gp_seq = rcu_state.gp_seq;
local_irq_restore(flags);
}
EXPORT_SYMBOL_GPL(synchronize_rcu);