diff options
| author | Frederic Weisbecker <frederic@kernel.org> | 2024-05-15 14:53:32 +0200 |
|---|---|---|
| committer | Paul E. McKenney <paulmck@kernel.org> | 2024-06-28 06:44:12 -0700 |
| commit | 677ab23bdf416ec8f3ecaf10d7cc8d0ccb46adab (patch) | |
| tree | 5cb19cf4715bee07250a4e0c0ffbf376c4ee0a2a /kernel/rcu | |
| parent | 55911a9f4287c19bf7ef29aeace14044a6ed88cb (diff) | |
rcu/exp: Remove redundant full memory barrier at the end of GP
A full memory barrier is necessary at the end of the expedited grace
period to order:
1) The grace period completion (pictured by the GP sequence
number) with all preceding accesses. This pairs with rcu_seq_end()
performed by the concurrent kworker.
2) The grace period completion and subsequent post-GP update side
accesses. Pairs again against rcu_seq_end().
This full barrier is already provided by the final sync_exp_work_done()
test, making the subsequent explicit one redundant. Remove it and
improve comments.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Reviewed-by: Neeraj Upadhyay <neeraj.upadhyay@kernel.org>
Diffstat (limited to 'kernel/rcu')
| -rw-r--r-- | kernel/rcu/tree_exp.h | 8 |
1 files changed, 6 insertions, 2 deletions
diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h index 1dbad2442e8d..4acd29d16fdb 100644 --- a/kernel/rcu/tree_exp.h +++ b/kernel/rcu/tree_exp.h @@ -265,7 +265,12 @@ static bool sync_exp_work_done(unsigned long s) { if (rcu_exp_gp_seq_done(s)) { trace_rcu_exp_grace_period(rcu_state.name, s, TPS("done")); - smp_mb(); /* Ensure test happens before caller kfree(). */ + /* + * Order GP completion with preceding accesses. Order also GP + * completion with post GP update side accesses. Pairs with + * rcu_seq_end(). + */ + smp_mb(); return true; } return false; @@ -967,7 +972,6 @@ void synchronize_rcu_expedited(void) rnp = rcu_get_root(); wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3], sync_exp_work_done(s)); - smp_mb(); /* Work actions happen before return. */ /* Let the next expedited grace period start. */ mutex_unlock(&rcu_state.exp_mutex); |