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rcu: Remove never-set needwake assignment from rcu_report_qs_rdp() 

The rcu_accelerate_cbs() function is invoked by rcu_report_qs_rdp()
only if there is a grace period in progress that is still blocked
by at least one CPU on this rcu_node structure.  This means that
rcu_accelerate_cbs() should never return the value true, and thus that
this function should never set the needwake variable and in turn never
invoke rcu_gp_kthread_wake().

This commit therefore removes the needwake variable and the invocation
of rcu_gp_kthread_wake() in favor of a WARN_ON_ONCE() on the call to
rcu_accelerate_cbs().  The purpose of this new WARN_ON_ONCE() is to
detect situations where the system's opinion differs from ours.

Signed-off-by: Zqiang <qiang1.zhang@intel.com>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Joel Fernandes (Google) <joel@joelfernandes.org>
This commit is contained in:
Zqiang 2023-01-18 15:30:14 +08:00 committed by Joel Fernandes (Google)
parent 2450b78e0b
commit 46103fe01b
1 changed files with 6 additions and 4 deletions
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10
kernel/rcu/tree.c
View File

@ -1955,7 +1955,6 @@ rcu_report_qs_rdp(struct rcu_data *rdp)
{
unsigned long flags;
unsigned long mask;
bool needwake = false;
bool needacc = false;
struct rcu_node *rnp;
@ -1987,7 +1986,12 @@ rcu_report_qs_rdp(struct rcu_data *rdp)
* NOCB kthreads have their own way to deal with that...
*/
if (!rcu_rdp_is_offloaded(rdp)) {
needwake = rcu_accelerate_cbs(rnp, rdp);
/*
* The current GP has not yet ended, so it
* should not be possible for rcu_accelerate_cbs()
* to return true. So complain, but don't awaken.
*/
WARN_ON_ONCE(rcu_accelerate_cbs(rnp, rdp));
} else if (!rcu_segcblist_completely_offloaded(&rdp->cblist)) {
/*
* ...but NOCB kthreads may miss or delay callbacks acceleration
@ -1999,8 +2003,6 @@ rcu_report_qs_rdp(struct rcu_data *rdp)
rcu_disable_urgency_upon_qs(rdp);
rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags);
/* ^^^ Released rnp->lock */
if (needwake)
rcu_gp_kthread_wake();
if (needacc) {
rcu_nocb_lock_irqsave(rdp, flags);