On Fri, Nov 20, 2020 at 05:06:50PM +0530, Neeraj Upadhyay wrote:
>
>
> On 11/17/2020 6:10 AM, [email protected] wrote:
> > From: "Paul E. McKenney" <[email protected]>
> >
> > There is a need for a polling interface for SRCU grace periods.
> > This polling needs to initiate an SRCU grace period without having
> > to queue (and manage) a callback. This commit therefore splits the
> > Tree SRCU __call_srcu() function into callback-initialization and
> > queuing/start-grace-period portions, with the latter in a new function
> > named srcu_gp_start_if_needed(). This function may be passed a NULL
> > callback pointer, in which case it will refrain from queuing anything.
> >
> > Why have the new function mess with queuing? Locking considerations,
> > of course!
> >
> > Link: https://lore.kernel.org/rcu/[email protected]/
> > Reported-by: Kent Overstreet <[email protected]>
> > Signed-off-by: Paul E. McKenney <[email protected]>
> > ---
>
> Reviewed-by: Neeraj Upadhyay <[email protected]>
I applied both Reviewed-bys, thank you!
Thanx, Paul
> Thanks
> Neeraj
>
> > kernel/rcu/srcutree.c | 66
> > +++++++++++++++++++++++++++++----------------------
> > 1 file changed, 37 insertions(+), 29 deletions(-)
> >
> > diff --git a/kernel/rcu/srcutree.c b/kernel/rcu/srcutree.c
> > index 79b7081..d930ece 100644
> > --- a/kernel/rcu/srcutree.c
> > +++ b/kernel/rcu/srcutree.c
> > @@ -808,6 +808,42 @@ static void srcu_leak_callback(struct rcu_head *rhp)
> > }
> > /*
> > + * Start an SRCU grace period, and also queue the callback if non-NULL.
> > + */
> > +static void srcu_gp_start_if_needed(struct srcu_struct *ssp, struct
> > rcu_head *rhp, bool do_norm)
> > +{
> > + unsigned long flags;
> > + int idx;
> > + bool needexp = false;
> > + bool needgp = false;
> > + unsigned long s;
> > + struct srcu_data *sdp;
> > +
> > + idx = srcu_read_lock(ssp);
> > + sdp = raw_cpu_ptr(ssp->sda);
> > + spin_lock_irqsave_rcu_node(sdp, flags);
> > + rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp);
> > + rcu_segcblist_advance(&sdp->srcu_cblist,
> > + rcu_seq_current(&ssp->srcu_gp_seq));
> > + s = rcu_seq_snap(&ssp->srcu_gp_seq);
> > + (void)rcu_segcblist_accelerate(&sdp->srcu_cblist, s);
> > + if (ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s)) {
> > + sdp->srcu_gp_seq_needed = s;
> > + needgp = true;
> > + }
> > + if (!do_norm && ULONG_CMP_LT(sdp->srcu_gp_seq_needed_exp, s)) {
> > + sdp->srcu_gp_seq_needed_exp = s;
> > + needexp = true;
> > + }
> > + spin_unlock_irqrestore_rcu_node(sdp, flags);
> > + if (needgp)
> > + srcu_funnel_gp_start(ssp, sdp, s, do_norm);
> > + else if (needexp)
> > + srcu_funnel_exp_start(ssp, sdp->mynode, s);
> > + srcu_read_unlock(ssp, idx);
> > +}
> > +
> > +/*
> > * Enqueue an SRCU callback on the srcu_data structure associated with
> > * the current CPU and the specified srcu_struct structure, initiating
> > * grace-period processing if it is not already running.
> > @@ -838,13 +874,6 @@ static void srcu_leak_callback(struct rcu_head *rhp)
> > static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
> > rcu_callback_t func, bool do_norm)
> > {
> > - unsigned long flags;
> > - int idx;
> > - bool needexp = false;
> > - bool needgp = false;
> > - unsigned long s;
> > - struct srcu_data *sdp;
> > -
> > check_init_srcu_struct(ssp);
> > if (debug_rcu_head_queue(rhp)) {
> > /* Probable double call_srcu(), so leak the callback. */
> > @@ -853,28 +882,7 @@ static void __call_srcu(struct srcu_struct *ssp,
> > struct rcu_head *rhp,
> > return;
> > }
> > rhp->func = func;
> > - idx = srcu_read_lock(ssp);
> > - sdp = raw_cpu_ptr(ssp->sda);
> > - spin_lock_irqsave_rcu_node(sdp, flags);
> > - rcu_segcblist_enqueue(&sdp->srcu_cblist, rhp);
> > - rcu_segcblist_advance(&sdp->srcu_cblist,
> > - rcu_seq_current(&ssp->srcu_gp_seq));
> > - s = rcu_seq_snap(&ssp->srcu_gp_seq);
> > - (void)rcu_segcblist_accelerate(&sdp->srcu_cblist, s);
> > - if (ULONG_CMP_LT(sdp->srcu_gp_seq_needed, s)) {
> > - sdp->srcu_gp_seq_needed = s;
> > - needgp = true;
> > - }
> > - if (!do_norm && ULONG_CMP_LT(sdp->srcu_gp_seq_needed_exp, s)) {
> > - sdp->srcu_gp_seq_needed_exp = s;
> > - needexp = true;
> > - }
> > - spin_unlock_irqrestore_rcu_node(sdp, flags);
> > - if (needgp)
> > - srcu_funnel_gp_start(ssp, sdp, s, do_norm);
> > - else if (needexp)
> > - srcu_funnel_exp_start(ssp, sdp->mynode, s);
> > - srcu_read_unlock(ssp, idx);
> > + srcu_gp_start_if_needed(ssp, rhp, do_norm);
> > }
> > /**
> >
>
> --
> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of
> the Code Aurora Forum, hosted by The Linux Foundation
