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From: Valentin Schneider <valentin.schneider@arm.com>
To: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org, rcu@vger.kernel.org,
	linux-rt-users@vger.kernel.org,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will@kernel.org>, Ingo Molnar <mingo@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Steven Rostedt <rostedt@goodmis.org>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	"Paul E. McKenney" <paulmck@kernel.org>,
	Frederic Weisbecker <frederic@kernel.org>,
	Josh Triplett <josh@joshtriplett.org>,
	Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Davidlohr Bueso <dave@stgolabs.net>,
	Lai Jiangshan <jiangshanlai@gmail.com>,
	Joel Fernandes <joel@joelfernandes.org>,
	Anshuman Khandual <anshuman.khandual@arm.com>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>,
	Steven Price <steven.price@arm.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Boqun Feng <boqun.feng@gmail.com>, Mike Galbraith <efault@gmx.de>
Subject: Re: [PATCH v3 3/4] rcu/nocb: Protect NOCB state via local_lock() under PREEMPT_RT
Date: Sun, 22 Aug 2021 19:15:32 +0100	[thread overview]
Message-ID: <87bl5p73cr.mognet@arm.com> (raw)
In-Reply-To: <20210817153613.l5f66czar6pajexo@linutronix.de>

On 17/08/21 17:36, Sebastian Andrzej Siewior wrote:
>> +static inline int rcu_lockdep_is_held_nocb_local(struct rcu_data *rdp)
>> +{
>> +	return lockdep_is_held(
>> +#ifdef CONFIG_PREEMPT_RT
>> +		&rdp->nocb_local_lock.lock
>> +#else
>> +		&rdp->nocb_local_lock
>> +#endif
>> +	);
>> +}
>
> Now that I see it and Paul asked for it, please just use !RT version.
>       return lockdep_is_held(&rdp->nocb_local_lock);
>
> and RT will work, too.
>

The above was required due to the (previous) definition of local_lock_t:

  typedef struct {
          spinlock_t		lock;
  } local_lock_t;

On -rt11 I see this is now:

  typedef spinlock_t local_lock_t;

which indeed means the iffdefery can (actually it *has* to) go.

>>  static inline bool rcu_current_is_nocb_kthread(struct rcu_data *rdp)
>>  {
>>      /* Race on early boot between thread creation and assignment */
>> @@ -1629,6 +1664,22 @@ static void rcu_nocb_unlock_irqrestore(struct rcu_data *rdp,
>>      }
>>  }
>>
>> +/*
>> + * The invocation of rcu_core() within the RCU core kthreads remains preemptible
>> + * under PREEMPT_RT, thus the offload state of a CPU could change while
>> + * said kthreads are preempted. Prevent this from happening by protecting the
>> + * offload state with a local_lock().
>> + */
>> +static void rcu_nocb_local_lock(struct rcu_data *rdp)
>> +{
>> +	local_lock(&rcu_data.nocb_local_lock);
>> +}
>> +
>> +static void rcu_nocb_local_unlock(struct rcu_data *rdp)
>> +{
>> +	local_unlock(&rcu_data.nocb_local_lock);
>> +}
>> +
> Do you need to pass rdp given that it is not used?
>

Not anymore, you're right.

>>  /* Lockdep check that ->cblist may be safely accessed. */
>>  static void rcu_lockdep_assert_cblist_protected(struct rcu_data *rdp)
>>  {
>
> Sebastian

  reply	other threads:[~2021-08-22 18:15 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-08-11 20:13 [PATCH v3 0/4] rcu, arm64: PREEMPT_RT fixlets Valentin Schneider
2021-08-11 20:13 ` [PATCH v3 1/4] rcutorture: Don't disable softirqs with preemption disabled when PREEMPT_RT Valentin Schneider
2021-08-12 16:47   ` Paul E. McKenney
2021-08-17 12:13   ` Sebastian Andrzej Siewior
2021-08-17 13:17     ` Sebastian Andrzej Siewior
2021-08-17 14:40       ` [PATCH] rcutorture: Avoid problematic critical section nesting on RT Sebastian Andrzej Siewior
2021-08-18 22:46         ` Paul E. McKenney
2021-08-19 15:35           ` Sebastian Andrzej Siewior
2021-08-19 15:39           ` Sebastian Andrzej Siewior
2021-08-19 15:47             ` Sebastian Andrzej Siewior
2021-08-19 18:20               ` Paul E. McKenney
2021-08-19 18:45                 ` Sebastian Andrzej Siewior
2021-08-20  4:11                 ` Scott Wood
2021-08-20  7:11                   ` Sebastian Andrzej Siewior
2021-08-20  7:42                   ` [PATCH v2] rcutorture: Avoid problematic critical section nesting on PREEMPT_RT Sebastian Andrzej Siewior
2021-08-20 22:10                     ` Paul E. McKenney
2021-08-20  3:23         ` [PATCH] rcutorture: Avoid problematic critical section nesting on RT Scott Wood
2021-08-20  6:54           ` Sebastian Andrzej Siewior
2021-08-11 20:13 ` [PATCH v3 2/4] sched: Introduce migratable() Valentin Schneider
2021-08-17 14:43   ` Sebastian Andrzej Siewior
2021-08-22 17:31     ` Valentin Schneider
2021-08-17 17:09   ` Sebastian Andrzej Siewior
2021-08-17 19:30     ` Phil Auld
2021-08-22 18:14     ` Valentin Schneider
2022-01-26 16:56       ` Sebastian Andrzej Siewior
2022-01-26 18:10         ` Valentin Schneider
2022-01-27 10:07           ` Sebastian Andrzej Siewior
2022-01-27 18:23             ` Valentin Schneider
2022-01-27 19:27         ` Valentin Schneider
2022-02-04  9:24           ` Sebastian Andrzej Siewior
2021-08-11 20:13 ` [PATCH v3 3/4] rcu/nocb: Protect NOCB state via local_lock() under PREEMPT_RT Valentin Schneider
2021-08-13  0:20   ` Paul E. McKenney
2021-08-13 18:48     ` Valentin Schneider
2021-08-24 13:00     ` Frederic Weisbecker
2021-08-17 15:36   ` Sebastian Andrzej Siewior
2021-08-22 18:15     ` Valentin Schneider [this message]
2021-09-21 14:05   ` Thomas Gleixner
2021-09-21 21:12     ` rcu/tree: Protect rcu_rdp_is_offloaded() invocations on RT Thomas Gleixner
2021-09-21 23:36       ` Frederic Weisbecker
2021-09-22  2:18         ` Paul E. McKenney
2021-09-22 11:31           ` Frederic Weisbecker
2021-09-21 23:45       ` Frederic Weisbecker
2021-09-22  6:32         ` Sebastian Andrzej Siewior
2021-09-22 11:10           ` Frederic Weisbecker
2021-09-22 11:27             ` Sebastian Andrzej Siewior
2021-09-22 11:38               ` Frederic Weisbecker
2021-09-22 13:02                 ` Sebastian Andrzej Siewior
2021-09-23 10:02                   ` Frederic Weisbecker
2021-09-30  9:00       ` Valentin Schneider
2021-09-30 10:53         ` Frederic Weisbecker
2021-09-30 13:22           ` Valentin Schneider
2021-08-11 20:13 ` [PATCH v3 4/4] arm64: mm: Make arch_faults_on_old_pte() check for migratability Valentin Schneider

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