From: Frederic Weisbecker <frederic@kernel.org>
To: "Paul E. McKenney" <paulmck@kernel.org>
Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
kernel-team@fb.com, mingo@kernel.org, jiangshanlai@gmail.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
Guillaume Morin <guillaume@morinfr.org>
Subject: Re: [PATCH rcu 01/18] rcu: Tighten rcu_advance_cbs_nowake() checks
Date: Thu, 2 Dec 2021 01:41:42 +0100 [thread overview]
Message-ID: <20211202004142.GA631289@lothringen> (raw)
In-Reply-To: <20211202002912.3127710-1-paulmck@kernel.org>
On Wed, Dec 01, 2021 at 04:28:55PM -0800, Paul E. McKenney wrote:
> Currently, rcu_advance_cbs_nowake() checks that a grace period is in
> progress, however, that grace period could end just after the check.
> This commit rechecks that a grace period is still in progress the lock.
*while holding the node lock.
> The grace period cannot end while the current CPU's rcu_node structure's
> ->lock is held, thus avoiding false positives from the WARN_ON_ONCE().
>
> As Daniel Vacek noted, it is not necessary for the rcu_node structure
> to have a CPU that has not yet passed through its quiescent state.
>
> Tested-By: Guillaume Morin <guillaume@morinfr.org>
> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Thanks!
> ---
> kernel/rcu/tree.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index ef8d36f580fc3..8706b30c2ac88 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -1590,10 +1590,11 @@ static void __maybe_unused rcu_advance_cbs_nowake(struct rcu_node *rnp,
> struct rcu_data *rdp)
> {
> rcu_lockdep_assert_cblist_protected(rdp);
> - if (!rcu_seq_state(rcu_seq_current(&rnp->gp_seq)) ||
> - !raw_spin_trylock_rcu_node(rnp))
> + if (!rcu_seq_state(rcu_seq_current(&rnp->gp_seq)) || !raw_spin_trylock_rcu_node(rnp))
> return;
> - WARN_ON_ONCE(rcu_advance_cbs(rnp, rdp));
> + // The grace period cannot end while we hold the rcu_node lock.
> + if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq)))
> + WARN_ON_ONCE(rcu_advance_cbs(rnp, rdp));
> raw_spin_unlock_rcu_node(rnp);
> }
>
> --
> 2.31.1.189.g2e36527f23
>
next prev parent reply other threads:[~2021-12-02 0:42 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-02 0:28 [PATCH rcu 0/18] RCU no-CBs CPU updates for v5.17 Paul E. McKenney
2021-12-02 0:28 ` [PATCH rcu 01/18] rcu: Tighten rcu_advance_cbs_nowake() checks Paul E. McKenney
2021-12-02 0:41 ` Frederic Weisbecker [this message]
2021-12-02 0:55 ` Paul E. McKenney
2021-12-02 0:28 ` [PATCH rcu 02/18] rcu/nocb: Make local rcu_nocb_lock_irqsave() safe against concurrent deoffloading Paul E. McKenney
2021-12-02 0:28 ` [PATCH rcu 03/18] rcu/nocb: Prepare state machine for a new step Paul E. McKenney
2021-12-02 0:28 ` [PATCH rcu 04/18] rcu/nocb: Invoke rcu_core() at the start of deoffloading Paul E. McKenney
2021-12-02 0:28 ` [PATCH rcu 05/18] rcu/nocb: Make rcu_core() callbacks acceleration preempt-safe Paul E. McKenney
2021-12-02 0:29 ` [PATCH rcu 06/18] rcu/nocb: Make rcu_core() callbacks acceleration (de-)offloading safe Paul E. McKenney
2021-12-02 0:29 ` [PATCH rcu 07/18] rcu/nocb: Check a stable offloaded state to manipulate qlen_last_fqs_check Paul E. McKenney
2021-12-02 0:29 ` [PATCH rcu 08/18] rcu/nocb: Use appropriate rcu_nocb_lock_irqsave() Paul E. McKenney
2021-12-02 0:29 ` [PATCH rcu 09/18] rcu/nocb: Limit number of softirq callbacks only on softirq Paul E. McKenney
2021-12-02 0:29 ` [PATCH rcu 10/18] rcu: Fix callbacks processing time limit retaining cond_resched() Paul E. McKenney
2021-12-02 0:29 ` [PATCH rcu 11/18] rcu: Apply callbacks processing time limit only on softirq Paul E. McKenney
2021-12-02 0:29 ` [PATCH rcu 12/18] rcu/nocb: Don't invoke local rcu core on callback overload from nocb kthread Paul E. McKenney
2021-12-02 0:29 ` [PATCH rcu 13/18] rcu/nocb: Remove rcu_node structure from nocb list when de-offloaded Paul E. McKenney
2021-12-02 0:29 ` [PATCH rcu 14/18] rcu/nocb: Prepare nocb_cb_wait() to start with a non-offloaded rdp Paul E. McKenney
2021-12-02 0:29 ` [PATCH rcu 15/18] rcu/nocb: Optimize kthreads and rdp initialization Paul E. McKenney
2021-12-02 0:29 ` [PATCH rcu 16/18] rcu/nocb: Create kthreads on all CPUs if "rcu_nocbs=" or "nohz_full=" are passed Paul E. McKenney
2021-12-02 0:29 ` [PATCH rcu 17/18] rcu/nocb: Allow empty "rcu_nocbs" kernel parameter Paul E. McKenney
2021-12-02 0:29 ` [PATCH rcu 18/18] rcu/nocb: Merge rcu_spawn_cpu_nocb_kthread() and rcu_spawn_one_nocb_kthread() Paul E. McKenney
2021-12-02 2:03 ` [PATCH rcu 0/18] RCU no-CBs CPU updates for v5.17 Yury Norov
2021-12-02 18:01 ` Paul E. McKenney
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