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Date: Thu, 9 Nov 2023 01:41:12 +0200
From: Vladimir Oltean <vladimir.oltean@....com>
To: Faizal Rahim <faizal.abdul.rahim@...ux.intel.com>
Cc: Vinicius Costa Gomes <vinicius.gomes@...el.com>,
Jamal Hadi Salim <jhs@...atatu.com>,
Cong Wang <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>,
"David S . Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 net 3/7] net/sched: taprio: update impacted fields
during cycle time adjustment
On Tue, Nov 07, 2023 at 06:20:19AM -0500, Faizal Rahim wrote:
> Update impacted fields in advance_sched() if cycle_corr_active()
> is true, which indicates that the next entry is the last entry
> from oper that it will run.
>
> Update impacted fields:
>
> 1. gate_duration[tc], max_open_gate_duration[tc]
> Created a new API update_open_gate_duration().The API sets the
> duration based on the last remaining entry, the original value
> was based on consideration of multiple entries.
>
> 2. gate_close_time[tc]
> Update next entry gate close time according to the new admin
> base time
>
> 3. max_sdu[tc], budget[tc]
> Restrict from setting to max value because there's only a single
> entry left to run from oper before changing to the new admin
> schedule, so we shouldn't set to max.
>
> Signed-off-by: Faizal Rahim <faizal.abdul.rahim@...ux.intel.com>
The commit message shouldn't be a text-to-speech output of the commit body.
Say very shortly how the system should behave, what's wrong such that it
doesn't behave as expected, what's the user-visible impact of the bug,
and try to identify why the bug happened.
In this case, what happened is that commit a306a90c8ffe ("net/sched:
taprio: calculate tc gate durations"), which introduced the impacted
fields you are changing, never took dynamic schedule changes into
consideration. So this commit should also appear in the Fixes: tag.
> ---
> net/sched/sch_taprio.c | 49 +++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 46 insertions(+), 3 deletions(-)
>
> diff --git a/net/sched/sch_taprio.c b/net/sched/sch_taprio.c
> index ed32654b46f5..119dec3bbe88 100644
> --- a/net/sched/sch_taprio.c
> +++ b/net/sched/sch_taprio.c
> @@ -288,7 +288,8 @@ static void taprio_update_queue_max_sdu(struct taprio_sched *q,
> /* TC gate never closes => keep the queueMaxSDU
> * selected by the user
> */
> - if (sched->max_open_gate_duration[tc] == sched->cycle_time) {
> + if (sched->max_open_gate_duration[tc] == sched->cycle_time &&
> + !cycle_corr_active(sched->cycle_time_correction)) {
> max_sdu_dynamic = U32_MAX;
> } else {
> u32 max_frm_len;
> @@ -684,7 +685,8 @@ static void taprio_set_budgets(struct taprio_sched *q,
>
> for (tc = 0; tc < num_tc; tc++) {
> /* Traffic classes which never close have infinite budget */
> - if (entry->gate_duration[tc] == sched->cycle_time)
> + if (entry->gate_duration[tc] == sched->cycle_time &&
> + !cycle_corr_active(sched->cycle_time_correction))
> budget = INT_MAX;
> else
> budget = div64_u64((u64)entry->gate_duration[tc] * PSEC_PER_NSEC,
> @@ -896,6 +898,32 @@ static bool should_restart_cycle(const struct sched_gate_list *oper,
> return false;
> }
>
> +/* Open gate duration were calculated at the beginning with consideration of
> + * multiple entries. If cycle time correction is active, there's only a single
> + * remaining entry left from oper to run.
> + * Update open gate duration based on this last entry.
> + */
> +static void update_open_gate_duration(struct sched_entry *entry,
> + struct sched_gate_list *oper,
> + int num_tc,
> + u64 open_gate_duration)
> +{
> + int tc;
> +
> + if (!entry || !oper)
> + return;
> +
> + for (tc = 0; tc < num_tc; tc++) {
> + if (entry->gate_mask & BIT(tc)) {
> + entry->gate_duration[tc] = open_gate_duration;
> + oper->max_open_gate_duration[tc] = open_gate_duration;
> + } else {
> + entry->gate_duration[tc] = 0;
> + oper->max_open_gate_duration[tc] = 0;
> + }
> + }
> +}
> +
> static bool should_change_sched(struct sched_gate_list *oper)
> {
> bool change_to_admin_sched = false;
> @@ -1010,13 +1038,28 @@ static enum hrtimer_restart advance_sched(struct hrtimer *timer)
> /* The next entry is the last entry we will run from
> * oper, subsequent ones will take from the new admin
> */
> + u64 new_gate_duration =
> + next->interval + oper->cycle_time_correction;
> + struct qdisc_size_table *stab =
> + rtnl_dereference(q->root->stab);
> +
The lockdep annotation for this RCU accessor is bogus.
rtnl_dereference() is the same as rcu_dereference_protected(..., lockdep_rtnl_is_held()),
which cannot be true in a hrtimer callback, as the rtnetlink lock is a
sleepable mutex and hrtimers run in atomic context.
Running with lockdep enabled will tell you as much:
$ ./test_taprio_cycle_extension.sh
Testing config change with a delay of 5250000000 ns between schedules
[ 100.734925]
[ 100.736703] =============================
[ 100.740780] WARNING: suspicious RCU usage
[ 100.744857] 6.6.0-10114-gca572939947f #1495 Not tainted
[ 100.750162] -----------------------------
[ 100.754236] net/sched/sch_taprio.c:1064 suspicious rcu_dereference_protected() usage!
[ 100.762155]
[ 100.762155] other info that might help us debug this:
[ 100.762155]
[ 100.770242]
[ 100.770242] rcu_scheduler_active = 2, debug_locks = 1
[ 100.776851] 1 lock held by swapper/0/0:
[ 100.780756] #0: ffff3d9784b83b00 (&q->current_entry_lock){-...}-{3:3}, at: advance_sched+0x44/0x59c
[ 100.790099]
[ 100.790099] stack backtrace:
[ 100.794477] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 6.6.0-10114-gca572939947f #1495
[ 100.802346] Hardware name: LS1028A RDB Board (DT)
[ 100.807072] Call trace:
[ 100.809531] dump_backtrace+0xf4/0x140
[ 100.813305] show_stack+0x18/0x2c
[ 100.816638] dump_stack_lvl+0x60/0x80
[ 100.820321] dump_stack+0x18/0x24
[ 100.823654] lockdep_rcu_suspicious+0x170/0x210
[ 100.828210] advance_sched+0x384/0x59c
[ 100.831978] __hrtimer_run_queues+0x200/0x430
[ 100.836360] hrtimer_interrupt+0xdc/0x39c
[ 100.840392] arch_timer_handler_phys+0x3c/0x4c
[ 100.844862] handle_percpu_devid_irq+0xb8/0x28c
[ 100.849417] generic_handle_domain_irq+0x2c/0x44
[ 100.854060] gic_handle_irq+0x4c/0x110
[ 100.857830] call_on_irq_stack+0x24/0x4c
[ 100.861775] el1_interrupt+0x74/0xc0
[ 100.865370] el1h_64_irq_handler+0x18/0x24
[ 100.869489] el1h_64_irq+0x64/0x68
[ 100.872909] arch_local_irq_enable+0x8/0xc
[ 100.877032] cpuidle_enter+0x38/0x50
[ 100.880629] do_idle+0x1ec/0x280
[ 100.883877] cpu_startup_entry+0x34/0x38
[ 100.887822] kernel_init+0x0/0x1a0
[ 100.891245] start_kernel+0x0/0x3b0
[ 100.894756] start_kernel+0x2f8/0x3b0
[ 100.898439] __primary_switched+0xbc/0xc4
What I would do is:
struct qdisc_size_table *stab;
rcu_read_lock();
stab = rcu_dereference(q->root->stab);
taprio_update_queue_max_sdu(q, oper, stab);
rcu_read_unlock();
> oper->cycle_end_time = new_base_time;
> end_time = new_base_time;
> +
> + update_open_gate_duration(next, oper, num_tc,
> + new_gate_duration);
> + taprio_update_queue_max_sdu(q, oper, stab);
> }
> }
>
> for (tc = 0; tc < num_tc; tc++) {
> - if (next->gate_duration[tc] == oper->cycle_time)
> + if (cycle_corr_active(oper->cycle_time_correction) &&
> + (next->gate_mask & BIT(tc)))
> + /* Set to the new base time, ensuring a smooth transition
> + * to the new schedule when the next entry finishes.
> + */
> + next->gate_close_time[tc] = end_time;
> + else if (next->gate_duration[tc] == oper->cycle_time)
> next->gate_close_time[tc] = KTIME_MAX;
> else
> next->gate_close_time[tc] = ktime_add_ns(entry->end_time,
> --
> 2.25.1
>
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