| Message ID | 20240515125332.9306-4-frederic@kernel.org (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | 6acd13812c2d647c4f056570e064a88924039b49 |
| Headers | show |
| Series | rcu: Remove several redundant memory barriers | expand |
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index 8a1d9c8bd9f7..bec24ea6777e 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -357,7 +357,13 @@ static void __sync_rcu_exp_select_node_cpus(struct rcu_exp_work *rewp) !(rnp->qsmaskinitnext & mask)) { mask_ofl_test |= mask; } else { - snap = rcu_dynticks_snap(cpu); + /* + * Full ordering against accesses prior current GP and + * also against current GP sequence number is enforced + * by current rnp locking with chained + * smp_mb__after_unlock_lock(). + */ + snap = ct_dynticks_cpu_acquire(cpu); if (rcu_dynticks_in_eqs(snap)) mask_ofl_test |= mask; else
When the grace period kthread checks the extended quiescent state counter of a CPU, full ordering is necessary to ensure that either: * If the GP kthread observes the remote target in an extended quiescent state, then that target must observe all accesses prior to the current grace period, including the current grace period sequence number, once it exits that extended quiescent state. or: * If the GP kthread observes the remote target NOT in an extended quiescent state, then the target further entering in an extended quiescent state must observe all accesses prior to the current grace period, including the current grace period sequence number, once it enters that extended quiescent state. This ordering is enforced through a full memory barrier placed right before taking the first EQS snapshot. However this is superfluous because the snapshot is taken while holding the target's rnp lock which provides the necessary ordering through its chain of smp_mb__after_unlock_lock(). Remove the needless explicit barrier before the snapshot and put a comment about the implicit barrier newly relied upon here. Signed-off-by: Frederic Weisbecker <frederic@kernel.org> --- kernel/rcu/tree_exp.h | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)