From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
To: Alan Huang <mmpgouride@gmail.com>,
paulmck@kernel.org, frederic@kernel.org,
neeraj.upadhyay@kernel.org, joel@joelfernandes.org,
josh@joshtriplett.org, boqun.feng@gmail.com, rostedt@goodmis.org,
jiangshanlai@gmail.com, qiang.zhang1211@gmail.com
Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] rcu: Remove unreachable logic
Date: Mon, 29 Apr 2024 13:43:10 -0400 [thread overview]
Message-ID: <bb48fdad-7a00-45da-b545-60517267a2c8@efficios.com> (raw)
In-Reply-To: <20240429173439.1685274-1-mmpgouride@gmail.com>
On 2024-04-29 13:34, Alan Huang wrote:
> call_rcu_core is only called from __call_rcu_common with interrupt
> disabled. This patch thus removes the unreachable logic and the would-be
> unused 'flags' parameter.
Nack.
call_rcu_core() receives a @flags parameter which are the _saved_ flags
as they were prior to local_irq_save().
This patch highlights a misunderstanding of what the code is actually
doing.
Thanks,
Mathieu
>
> Signed-off-by: Alan Huang <mmpgouride@gmail.com>
> ---
> kernel/rcu/tree.c | 35 ++---------------------------------
> 1 file changed, 2 insertions(+), 33 deletions(-)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index d5507ac1bbf1..b0ea2ebd7769 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -2983,7 +2983,7 @@ static void rcutree_enqueue(struct rcu_data *rdp, struct rcu_head *head, rcu_cal
> * Handle any core-RCU processing required by a call_rcu() invocation.
> */
> static void call_rcu_core(struct rcu_data *rdp, struct rcu_head *head,
> - rcu_callback_t func, unsigned long flags)
> + rcu_callback_t func)
> {
> rcutree_enqueue(rdp, head, func);
> /*
> @@ -2992,37 +2992,6 @@ static void call_rcu_core(struct rcu_data *rdp, struct rcu_head *head,
> */
> if (!rcu_is_watching())
> invoke_rcu_core();
> -
> - /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
> - if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
> - return;
> -
> - /*
> - * Force the grace period if too many callbacks or too long waiting.
> - * Enforce hysteresis, and don't invoke rcu_force_quiescent_state()
> - * if some other CPU has recently done so. Also, don't bother
> - * invoking rcu_force_quiescent_state() if the newly enqueued callback
> - * is the only one waiting for a grace period to complete.
> - */
> - if (unlikely(rcu_segcblist_n_cbs(&rdp->cblist) >
> - rdp->qlen_last_fqs_check + qhimark)) {
> -
> - /* Are we ignoring a completed grace period? */
> - note_gp_changes(rdp);
> -
> - /* Start a new grace period if one not already started. */
> - if (!rcu_gp_in_progress()) {
> - rcu_accelerate_cbs_unlocked(rdp->mynode, rdp);
> - } else {
> - /* Give the grace period a kick. */
> - rdp->blimit = DEFAULT_MAX_RCU_BLIMIT;
> - if (READ_ONCE(rcu_state.n_force_qs) == rdp->n_force_qs_snap &&
> - rcu_segcblist_first_pend_cb(&rdp->cblist) != head)
> - rcu_force_quiescent_state();
> - rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs);
> - rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
> - }
> - }
> }
>
> /*
> @@ -3121,7 +3090,7 @@ __call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy_in)
> if (unlikely(rcu_rdp_is_offloaded(rdp)))
> call_rcu_nocb(rdp, head, func, flags, lazy);
> else
> - call_rcu_core(rdp, head, func, flags);
> + call_rcu_core(rdp, head, func);
> local_irq_restore(flags);
> }
>
--
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com
prev parent reply other threads:[~2024-04-29 17:51 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-29 17:34 [PATCH] rcu: Remove unreachable logic Alan Huang
2024-04-29 17:43 ` Mathieu Desnoyers [this message]
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