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SubjectRe: [PATCH 4/4] rcu: Name internal polling flag
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On 3/16/2022 8:12 PM, Frederic Weisbecker wrote:
> Give a proper self-explanatory name to the expedited grace period
> internal polling flag.
>
> Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
> Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com>
> Cc: Boqun Feng <boqun.feng@gmail.com>
> Cc: Uladzislau Rezki <uladzislau.rezki@sony.com>
> Cc: Joel Fernandes <joel@joelfernandes.org>
> ---
> kernel/rcu/rcu.h | 5 +++++
> kernel/rcu/tree.c | 2 +-
> kernel/rcu/tree_exp.h | 9 +++++----
> 3 files changed, 11 insertions(+), 5 deletions(-)
>
> diff --git a/kernel/rcu/rcu.h b/kernel/rcu/rcu.h
> index eccbdbdaa02e..8a62bb416ba4 100644
> --- a/kernel/rcu/rcu.h
> +++ b/kernel/rcu/rcu.h
> @@ -30,6 +30,11 @@
> #define RCU_GET_STATE_USE_NORMAL 0x2
> #define RCU_GET_STATE_BAD_FOR_NORMAL (RCU_GET_STATE_FROM_EXPEDITED | RCU_GET_STATE_USE_NORMAL)
>
> +/*
> + * Low-order bit definitions for polled grace-period internals.
> + */
> +#define RCU_EXP_SEQ_POLL_DONE 0x1

From what I understood, this flag is intended for lifecycle management
of the ->exp_seq_poll_rq; with the flag set meaning that we need to
re-poll, which could be used for cases, where there is long gap between
2 polls, such that the sequence wraps around. So, maybe we can name it
as RCU_EXP_SEQ_POLL_EXPIRED? However, my understanding could be wrong here.


Thanks
Neeraj

> +
> /*
> * Return the counter portion of a sequence number previously returned
> * by rcu_seq_snap() or rcu_seq_current().
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 5da381a3cbe5..b3223b365f9f 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -4679,7 +4679,7 @@ static void __init rcu_init_one(void)
> spin_lock_init(&rnp->exp_lock);
> mutex_init(&rnp->boost_kthread_mutex);
> raw_spin_lock_init(&rnp->exp_poll_lock);
> - rnp->exp_seq_poll_rq = 0x1;
> + rnp->exp_seq_poll_rq = RCU_EXP_SEQ_POLL_DONE;
> INIT_WORK(&rnp->exp_poll_wq, sync_rcu_do_polled_gp);
> }
> }
> diff --git a/kernel/rcu/tree_exp.h b/kernel/rcu/tree_exp.h
> index c4a19c6a83cf..7ccb909d6355 100644
> --- a/kernel/rcu/tree_exp.h
> +++ b/kernel/rcu/tree_exp.h
> @@ -910,14 +910,14 @@ static void sync_rcu_do_polled_gp(struct work_struct *wp)
> unsigned long s;
>
> s = READ_ONCE(rnp->exp_seq_poll_rq);
> - if (s & 0x1)
> + if (s & RCU_EXP_SEQ_POLL_DONE)
> return;
> while (!sync_exp_work_done(s))
> __synchronize_rcu_expedited(true);
> raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
> s = rnp->exp_seq_poll_rq;
> - if (!(s & 0x1) && sync_exp_work_done(s))
> - WRITE_ONCE(rnp->exp_seq_poll_rq, s | 0x1);
> + if (!(s & RCU_EXP_SEQ_POLL_DONE) && sync_exp_work_done(s))
> + WRITE_ONCE(rnp->exp_seq_poll_rq, s | RCU_EXP_SEQ_POLL_DONE);
> raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
> }
>
> @@ -946,7 +946,8 @@ unsigned long start_poll_synchronize_rcu_expedited(void)
> rnp = rdp->mynode;
> if (rcu_init_invoked())
> raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags);
> - if ((rnp->exp_seq_poll_rq & 0x1) || ULONG_CMP_LT(rnp->exp_seq_poll_rq, s)) {
> + if ((rnp->exp_seq_poll_rq & RCU_EXP_SEQ_POLL_DONE) ||
> + ULONG_CMP_LT(rnp->exp_seq_poll_rq, s)) {
> WRITE_ONCE(rnp->exp_seq_poll_rq, s);
> if (rcu_init_invoked())
> queue_work(rcu_gp_wq, &rnp->exp_poll_wq);

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