Messages in this thread | | | Subject | Re: [PATCH RFC tip/core/rcu 3/5] srcu: Provide internal interface to start a Tree SRCU grace period | From | Neeraj Upadhyay <> | Date | Fri, 20 Nov 2020 17:06:50 +0530 |
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On 11/17/2020 6:10 AM, paulmck@kernel.org wrote: > From: "Paul E. McKenney" <paulmck@kernel.org> > > 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@moria.home.lan/ > Reported-by: Kent Overstreet <kent.overstreet@gmail.com> > Signed-off-by: Paul E. McKenney <paulmck@kernel.org> > ---
Reviewed-by: Neeraj Upadhyay <neeraju@codeaurora.org>
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); > } > > /** >
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