On Fri, Nov 20, 2020 at 05:06:50PM +0530, Neeraj Upadhyay wrote: > > > On 11/17/2020 6:10 AM, paulmck@xxxxxxxxxx wrote: > > From: "Paul E. McKenney" <paulmck@xxxxxxxxxx> > > > > 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/20201112201547.GF3365678@xxxxxxxxxxxxxx/ > > Reported-by: Kent Overstreet <kent.overstreet@xxxxxxxxx> > > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> > > --- > > Reviewed-by: Neeraj Upadhyay <neeraju@xxxxxxxxxxxxxx> 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
