> On Jan 12, 2023, at 2:27 PM, Paul E. McKenney <paulmck@xxxxxxxxxx> wrote:
>
> On Thu, Jan 12, 2023 at 12:52:22AM +0000, Joel Fernandes (Google) wrote:
>> During boot and suspend/resume, it is desired to prevent RCU laziness from
>> effecting performance and in some cases failures like with suspend.
>>
>> Track whether RCU laziness is to be ignored or not, in kernels with
>> CONFIG_RCU_LAZY enabled. We do such tracking for expedited-RCU already, however
>> since Android currently expedites synchronous_rcu() always, we cannot rely on
>> that. The next patch ignores laziness hints based on this tracking.
>>
>> Signed-off-by: Joel Fernandes (Google) <joel@xxxxxxxxxxxxxxxxx>
>> ---
>> Paul, could we take this and the next one for 6.2 -rc cycle?
>>
>> I also booted debian Linux and verified the flag is reset correctly after boot
>> completes. Thanks.
>
> After going back and forth a bit, I took these two as-is (aside from
> the usual commit-log wordsmithing).
>
> At some point, the state-change-notification from things like boot,
> suspend/resume, sysrq-t, and panic() should probably be refactored.
> But I do not believe that we are yet at that point, and there is not
> much point in half-refactorings in cases such as this one.
>
> I added the Fixes tags, and, if testing goes well, I plan to submit
> them into the upcoming merge window. I have no reason to believe that
> anyone is hitting this, it is only a few weeks away anyhow, and a good
> chunk of that would be consumed by testing and review.
>
> And if someone does hit it, we do have your fixes to send to them, so
> thank you for that!
> (These won't become visible on -rcu until I complete today's rebase,
> in case you were wondering.)
Thanks and this sounds good to me. Meanwhile I pulled into our product kernel so all is good.
Thanks,
- Joel
>
> Thanx, Paul
>
>> kernel/rcu/rcu.h | 6 ++++++
>> kernel/rcu/tree.c | 2 ++
>> kernel/rcu/update.c | 40 +++++++++++++++++++++++++++++++++++++++-
>> 5 files changed, 55 insertions(+), 1 deletion(-)
>> create mode 100644 cc_list
>> create mode 100644 to_list
>>
>> diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
>> index 5c8013f7085f..115616ac3bfa 100644
>> --- a/kernel/rcu/rcu.h
>> +++ b/kernel/rcu/rcu.h
>> @@ -449,14 +449,20 @@ do { \
>> /* Tiny RCU doesn't expedite, as its purpose in life is instead to be tiny. */
>> static inline bool rcu_gp_is_normal(void) { return true; }
>> static inline bool rcu_gp_is_expedited(void) { return false; }
>> +static inline bool rcu_async_should_hurry(void) { return false; }
>> static inline void rcu_expedite_gp(void) { }
>> static inline void rcu_unexpedite_gp(void) { }
>> +static inline void rcu_async_hurry(void) { }
>> +static inline void rcu_async_relax(void) { }
>> static inline void rcu_request_urgent_qs_task(struct task_struct *t) { }
>> #else /* #ifdef CONFIG_TINY_RCU */
>> bool rcu_gp_is_normal(void); /* Internal RCU use. */
>> bool rcu_gp_is_expedited(void); /* Internal RCU use. */
>> +bool rcu_async_should_hurry(void); /* Internal RCU use. */
>> void rcu_expedite_gp(void);
>> void rcu_unexpedite_gp(void);
>> +void rcu_async_hurry(void);
>> +void rcu_async_relax(void);
>> void rcupdate_announce_bootup_oddness(void);
>> #ifdef CONFIG_TASKS_RCU_GENERIC
>> void show_rcu_tasks_gp_kthreads(void);
>> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
>> index 63545d79da51..78b2e999c904 100644
>> --- a/kernel/rcu/tree.c
>> +++ b/kernel/rcu/tree.c
>> @@ -4504,11 +4504,13 @@ static int rcu_pm_notify(struct notifier_block *self,
>> switch (action) {
>> case PM_HIBERNATION_PREPARE:
>> case PM_SUSPEND_PREPARE:
>> + rcu_async_hurry();
>> rcu_expedite_gp();
>> break;
>> case PM_POST_HIBERNATION:
>> case PM_POST_SUSPEND:
>> rcu_unexpedite_gp();
>> + rcu_async_relax();
>> break;
>> default:
>> break;
>> diff --git a/kernel/rcu/update.c b/kernel/rcu/update.c
>> index 3893022f8ed8..19bf6fa3ee6a 100644
>> --- a/kernel/rcu/update.c
>> +++ b/kernel/rcu/update.c
>> @@ -144,8 +144,45 @@ bool rcu_gp_is_normal(void)
>> }
>> EXPORT_SYMBOL_GPL(rcu_gp_is_normal);
>>
>> -static atomic_t rcu_expedited_nesting = ATOMIC_INIT(1);
>> +static atomic_t rcu_async_hurry_nesting = ATOMIC_INIT(1);
>> +/*
>> + * Should call_rcu() callbacks be processed with urgency or are
>> + * they OK being executed with arbitrary delays?
>> + */
>> +bool rcu_async_should_hurry(void)
>> +{
>> + return !IS_ENABLED(CONFIG_RCU_LAZY) ||
>> + atomic_read(&rcu_async_hurry_nesting);
>> +}
>> +EXPORT_SYMBOL_GPL(rcu_async_should_hurry);
>> +
>> +/**
>> + * rcu_async_hurry - Make future async RCU callbacks not lazy.
>> + *
>> + * After a call to this function, future calls to call_rcu()
>> + * will be processed in a timely fashion.
>> + */
>> +void rcu_async_hurry(void)
>> +{
>> + if (IS_ENABLED(CONFIG_RCU_LAZY))
>> + atomic_inc(&rcu_async_hurry_nesting);
>> +}
>> +EXPORT_SYMBOL_GPL(rcu_async_hurry);
>>
>> +/**
>> + * rcu_async_relax - Make future async RCU callbacks lazy.
>> + *
>> + * After a call to this function, future calls to call_rcu()
>> + * will be processed in a lazy fashion.
>> + */
>> +void rcu_async_relax(void)
>> +{
>> + if (IS_ENABLED(CONFIG_RCU_LAZY))
>> + atomic_dec(&rcu_async_hurry_nesting);
>> +}
>> +EXPORT_SYMBOL_GPL(rcu_async_relax);
>> +
>> +static atomic_t rcu_expedited_nesting = ATOMIC_INIT(1);
>> /*
>> * Should normal grace-period primitives be expedited? Intended for
>> * use within RCU. Note that this function takes the rcu_expedited
>> @@ -195,6 +232,7 @@ static bool rcu_boot_ended __read_mostly;
>> void rcu_end_inkernel_boot(void)
>> {
>> rcu_unexpedite_gp();
>> + rcu_async_relax();
>> if (rcu_normal_after_boot)
>> WRITE_ONCE(rcu_normal, 1);
>> rcu_boot_ended = true;
>> --
>> 2.39.0.314.g84b9a713c41-goog
