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author | Joel Fernandes (Google) <joel@joelfernandes.org> | 2018-05-23 08:38:13 +0200 |
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committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2018-07-13 00:39:20 +0200 |
commit | 0d805a70a652a6eef8d0283e5183879e7acb85ad (patch) | |
tree | a47046bbc2e0808ccfe4e34a33735e76bd40f6fe /kernel | |
parent | rcu: Use RCU CPU stall timeout for rcu_check_gp_start_stall() (diff) | |
download | linux-0d805a70a652a6eef8d0283e5183879e7acb85ad.tar.xz linux-0d805a70a652a6eef8d0283e5183879e7acb85ad.zip |
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) <joel@joelfernandes.org>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
[ paulmck: Shrink comment as suggested by Peter Zijlstra. ]
Diffstat (limited to 'kernel')
-rw-r--r-- | kernel/rcu/rcu.h | 12 |
1 files changed, 11 insertions, 1 deletions
diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h index aa215d6355f8..89f13fffac73 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; |