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rcu: Remove rcu_data.exp_deferred_qs and convert to rcu_data.cpu no_qs.b.exp

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Having two fields for the same purpose with subtle differences on
different RCU flavours is confusing, especially when both fields always
exist on both RCU flavours.

Fortunately, it is now safe for preemptible RCU to rely on the rcu_data
structure's ->cpu_no_qs.b.exp field, just like non-preemptible RCU.
This commit therefore removes the ad-hoc ->exp_deferred_qs field.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Frederic Weisbecker 2021-09-16 14:10:48 +02:00 committed by Paul E. McKenney
parent 6e16b0f7ba
commit 6120b72e25
3 changed files with 8 additions and 10 deletions
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1
kernel/rcu/tree.h
View File

@ -157,7 +157,6 @@ struct rcu_data {
bool core_needs_qs; /* Core waits for quiescent state. */
bool beenonline; /* CPU online at least once. */
bool gpwrap; /* Possible ->gp_seq wrap. */
bool exp_deferred_qs; /* This CPU awaiting a deferred QS? */
bool cpu_started; /* RCU watching this onlining CPU. */
struct rcu_node *mynode; /* This CPU's leaf of hierarchy */
unsigned long grpmask; /* Mask to apply to leaf qsmask. */

5
kernel/rcu/tree_exp.h
View File

@ -255,7 +255,6 @@ static void rcu_report_exp_cpu_mult(struct rcu_node *rnp,
*/
static void rcu_report_exp_rdp(struct rcu_data *rdp)
{
WRITE_ONCE(rdp->exp_deferred_qs, false);
WRITE_ONCE(rdp->cpu_no_qs.b.exp, false);
rcu_report_exp_cpu_mult(rdp->mynode, rdp->grpmask, true);
}
@ -656,7 +655,7 @@ static void rcu_exp_handler(void *unused)
rcu_dynticks_curr_cpu_in_eqs()) {
rcu_report_exp_rdp(rdp);
} else {
rdp->exp_deferred_qs = true;
WRITE_ONCE(rdp->cpu_no_qs.b.exp, true);
set_tsk_need_resched(t);
set_preempt_need_resched();
}
@ -678,7 +677,7 @@ static void rcu_exp_handler(void *unused)
if (depth > 0) {
raw_spin_lock_irqsave_rcu_node(rnp, flags);
if (rnp->expmask & rdp->grpmask) {
rdp->exp_deferred_qs = true;
WRITE_ONCE(rdp->cpu_no_qs.b.exp, true);
t->rcu_read_unlock_special.b.exp_hint = true;
}
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);

12
kernel/rcu/tree_plugin.h
View File

@ -260,10 +260,10 @@ static void rcu_preempt_ctxt_queue(struct rcu_node *rnp, struct rcu_data *rdp)
* no need to check for a subsequent expedited GP. (Though we are
* still in a quiescent state in any case.)
*/
if (blkd_state & RCU_EXP_BLKD && rdp->exp_deferred_qs)
if (blkd_state & RCU_EXP_BLKD && rdp->cpu_no_qs.b.exp)
rcu_report_exp_rdp(rdp);
else
WARN_ON_ONCE(rdp->exp_deferred_qs);
WARN_ON_ONCE(rdp->cpu_no_qs.b.exp);
}
/*
@ -354,7 +354,7 @@ void rcu_note_context_switch(bool preempt)
* means that we continue to block the current grace period.
*/
rcu_qs();
if (rdp->exp_deferred_qs)
if (rdp->cpu_no_qs.b.exp)
rcu_report_exp_rdp(rdp);
rcu_tasks_qs(current, preempt);
trace_rcu_utilization(TPS("End context switch"));
@ -481,7 +481,7 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
*/
special = t->rcu_read_unlock_special;
rdp = this_cpu_ptr(&rcu_data);
if (!special.s && !rdp->exp_deferred_qs) {
if (!special.s && !rdp->cpu_no_qs.b.exp) {
local_irq_restore(flags);
return;
}
@ -501,7 +501,7 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
* tasks are handled when removing the task from the
* blocked-tasks list below.
*/
if (rdp->exp_deferred_qs)
if (rdp->cpu_no_qs.b.exp)
rcu_report_exp_rdp(rdp);
/* Clean up if blocked during RCU read-side critical section. */
@ -584,7 +584,7 @@ rcu_preempt_deferred_qs_irqrestore(struct task_struct *t, unsigned long flags)
*/
static bool rcu_preempt_need_deferred_qs(struct task_struct *t)
{
return (__this_cpu_read(rcu_data.exp_deferred_qs) ||
return (__this_cpu_read(rcu_data.cpu_no_qs.b.exp) ||
READ_ONCE(t->rcu_read_unlock_special.s)) &&
rcu_preempt_depth() == 0;
}