From 0d805a70a652a6eef8d0283e5183879e7acb85ad Mon Sep 17 00:00:00 2001 From: "Joel Fernandes (Google)" Date: Tue, 22 May 2018 23:38:13 -0700 Subject: [PATCH] rcu: Add comment documenting how rcu_seq_snap works rcu_seq_snap may be tricky to decipher. Lets document how it works with an example to make it easier. Signed-off-by: Joel Fernandes (Google) Signed-off-by: Paul E. McKenney [ paulmck: Shrink comment as suggested by Peter Zijlstra. ] --- kernel/rcu/rcu.h | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h index aa215d6..89f13ff 100644 --- a/kernel/rcu/rcu.h +++ b/kernel/rcu/rcu.h @@ -91,7 +91,17 @@ static inline void rcu_seq_end(unsigned long *sp) WRITE_ONCE(*sp, rcu_seq_endval(sp)); } -/* Take a snapshot of the update side's sequence number. */ +/* + * rcu_seq_snap - Take a snapshot of the update side's sequence number. + * + * This function returns the earliest value of the grace-period sequence number + * that will indicate that a full grace period has elapsed since the current + * time. Once the grace-period sequence number has reached this value, it will + * be safe to invoke all callbacks that have been registered prior to the + * current time. This value is the current grace-period number plus two to the + * power of the number of low-order bits reserved for state, then rounded up to + * the next value in which the state bits are all zero. + */ static inline unsigned long rcu_seq_snap(unsigned long *sp) { unsigned long s; -- 2.7.4