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McKenney" To: "Uladzislau Rezki (Sony)" Cc: LKML , linux-mm@kvack.org, Andrew Morton , "Theodore Y . Ts'o" , Matthew Wilcox , Joel Fernandes , RCU , Oleksiy Avramchenko , Sebastian Andrzej Siewior Subject: Re: [PATCH 08/24] rcu/tree: Use static initializer for krc.lock Message-ID: <20200501211703.GC7560@paulmck-ThinkPad-P72> Reply-To: paulmck@kernel.org References: <20200428205903.61704-1-urezki@gmail.com> <20200428205903.61704-9-urezki@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200428205903.61704-9-urezki@gmail.com> User-Agent: Mutt/1.9.4 (2018-02-28) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Apr 28, 2020 at 10:58:47PM +0200, Uladzislau Rezki (Sony) wrote: > From: Sebastian Andrzej Siewior > > The per-CPU variable is initialized at runtime in > kfree_rcu_batch_init(). This function is invoked before > 'rcu_scheduler_active' is set to 'RCU_SCHEDULER_RUNNING'. > After the initialisation, '->initialized' is to true. > > The raw_spin_lock is only acquired if '->initialized' is > set to true. The worqueue item is only used if 'rcu_scheduler_active' > set to RCU_SCHEDULER_RUNNING which happens after initialisation. > > Use a static initializer for krc.lock and remove the runtime > initialisation of the lock. Since the lock can now be always > acquired, remove the '->initialized' check. > > Signed-off-by: Sebastian Andrzej Siewior > Signed-off-by: Uladzislau Rezki (Sony) > --- > kernel/rcu/tree.c | 15 +++++++-------- > 1 file changed, 7 insertions(+), 8 deletions(-) > > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c > index bc6c2bc8fa32..89e9ca3f4e3e 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -2892,7 +2892,7 @@ struct kfree_rcu_cpu_work { > * @lock: Synchronize access to this structure > * @monitor_work: Promote @head to @head_free after KFREE_DRAIN_JIFFIES > * @monitor_todo: Tracks whether a @monitor_work delayed work is pending > - * @initialized: The @lock and @rcu_work fields have been initialized > + * @initialized: The @rcu_work fields have been initialized > * > * This is a per-CPU structure. The reason that it is not included in > * the rcu_data structure is to permit this code to be extracted from > @@ -2912,7 +2912,9 @@ struct kfree_rcu_cpu { > int count; > }; > > -static DEFINE_PER_CPU(struct kfree_rcu_cpu, krc); > +static DEFINE_PER_CPU(struct kfree_rcu_cpu, krc) = { > + .lock = __RAW_SPIN_LOCK_UNLOCKED(krc.lock), > +}; > > static __always_inline void > debug_rcu_bhead_unqueue(struct kfree_rcu_bulk_data *bhead) > @@ -2930,10 +2932,9 @@ krc_this_cpu_lock(unsigned long *flags) > { > struct kfree_rcu_cpu *krcp; > > - local_irq_save(*flags); // For safely calling this_cpu_ptr(). > + local_irq_save(*flags); /* For safely calling this_cpu_ptr(). */ And here as well. ;-) Thanx, Paul > krcp = this_cpu_ptr(&krc); > - if (likely(krcp->initialized)) > - raw_spin_lock(&krcp->lock); > + raw_spin_lock(&krcp->lock); > > return krcp; > } > @@ -2941,8 +2942,7 @@ krc_this_cpu_lock(unsigned long *flags) > static inline void > krc_this_cpu_unlock(struct kfree_rcu_cpu *krcp, unsigned long flags) > { > - if (likely(krcp->initialized)) > - raw_spin_unlock(&krcp->lock); > + raw_spin_unlock(&krcp->lock); > local_irq_restore(flags); > } > > @@ -4168,7 +4168,6 @@ static void __init kfree_rcu_batch_init(void) > for_each_possible_cpu(cpu) { > struct kfree_rcu_cpu *krcp = per_cpu_ptr(&krc, cpu); > > - raw_spin_lock_init(&krcp->lock); > for (i = 0; i < KFREE_N_BATCHES; i++) { > INIT_RCU_WORK(&krcp->krw_arr[i].rcu_work, kfree_rcu_work); > krcp->krw_arr[i].krcp = krcp; > -- > 2.20.1 >