Commit 7f453536 authored by Paul E. McKenney's avatar Paul E. McKenney
Browse files

rcu: Make Tiny RCU grace periods visible to polled APIs 

This commit makes the Tiny RCU implementation of synchronize_rcu()
increment the rcu_ctrlblk.gp_seq counter, thus making both
synchronize_rcu() and synchronize_rcu_expedited() visible to
get_state_synchronize_rcu() and friends.

Link: https://lore.kernel.org/all/20220121142454.1994916-1-bfoster@redhat.com/
Link: https://docs.google.com/document/d/1RNKWW9jQyfjxw2E8dsXVTdvZYh0HnYeSHDKog9jhdN8/edit?usp=sharing


Cc: Brian Foster <bfoster@redhat.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Ian Kent <raven@themaw.net>
Signed-off-by: default avatarPaul E. McKenney <paulmck@kernel.org>
parent dd041405

kernel/rcu/tiny.c

+5 −2
Original line number Diff line number Diff line
@@ -139,8 +139,10 @@ static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused 
/*

 * Wait for a grace period to elapse.  But it is illegal to invoke

 * synchronize_rcu() from within an RCU read-side critical section.

 * Therefore, any legal call to synchronize_rcu() is a quiescent

 * state, and so on a UP system, synchronize_rcu() need do nothing.

 * Therefore, any legal call to synchronize_rcu() is a quiescent state,

 * and so on a UP system, synchronize_rcu() need do nothing, other than

 * let the polled APIs know that another grace period elapsed.

 *

 * (But Lai Jiangshan points out the benefits of doing might_sleep()

 * to reduce latency.)

 *
@@ -152,6 +154,7 @@ void synchronize_rcu(void) 
			 lock_is_held(&rcu_lock_map) ||

			 lock_is_held(&rcu_sched_lock_map),

			 "Illegal synchronize_rcu() in RCU read-side critical section");

	WRITE_ONCE(rcu_ctrlblk.gp_seq, rcu_ctrlblk.gp_seq + 2);

}

EXPORT_SYMBOL_GPL(synchronize_rcu);