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srcu: Provide internal interface to start a Tree SRCU grace period

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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>
Reviewed-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2020-11-13 10:08:09 -08:00
parent 1a893c711a
commit 29d2bb94a8
1 changed files with 37 additions and 29 deletions
Download patch file Download diff file Expand all files Collapse all files

66
kernel/rcu/srcutree.c
View file

@ -807,6 +807,42 @@ 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 * Enqueue an SRCU callback on the srcu_data structure associated with
* the current CPU and the specified srcu_struct structure, initiating * the current CPU and the specified srcu_struct structure, initiating
@ -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, static void __call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
rcu_callback_t func, bool do_norm) 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); check_init_srcu_struct(ssp);
if (debug_rcu_head_queue(rhp)) { if (debug_rcu_head_queue(rhp)) {
/* Probable double call_srcu(), so leak the callback. */ /* 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; return;
} }
rhp->func = func; rhp->func = func;
idx = srcu_read_lock(ssp); srcu_gp_start_if_needed(ssp, rhp, do_norm);
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);
} }
/** /**