From 7f4535366f8f77b3ddbc79d4ba82df966c5c2aab Mon Sep 17 00:00:00 2001 From: "Paul E. McKenney" Date: Thu, 14 Apr 2022 11:49:58 -0700 Subject: 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 Cc: Dave Chinner Cc: Al Viro Cc: Ian Kent Signed-off-by: Paul E. McKenney --- kernel/rcu/tiny.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/kernel/rcu/tiny.c b/kernel/rcu/tiny.c index dbee6bea6726..60071817d939 100644 --- a/kernel/rcu/tiny.c +++ b/kernel/rcu/tiny.c @@ -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); -- cgit v1.2.3-59-g8ed1b