tree 8607f866e4b084c3a18c7a8c5828d2fcff7aa12a
parent 7ceb54c9908b1ac1857e3eb08993b704a04116cc
author Paul E. McKenney <paulmck@kernel.org> 1632938974 -0700
committer Paul E. McKenney <paulmck@kernel.org> 1632938974 -0700

rcu: Make idle entry report expedited quiescent states

In non-preemptible kernels, an unfortunately timed expedited grace period
can result in the rcu_exp_handler() IPI handler setting the rcu_data
structure's cpu_no_qs.b.exp field just as the target CPU enters idle.
There are situations in which this field will not be checked until after
that CPU exits idle.  The resulting grace-period latency does not qualify
as "expedited".

This commit therefore checks this field upon non-preemptible idle entry in
the rcu_preempt_deferred_qs() function.  It also qualifies the rcu_core()
preempt_count() check with IS_ENABLED(CONFIG_PREEMPT_COUNT) to prevent
false-positive quiescent states from count-free kernels.

Reported-by: Neeraj Upadhyay <neeraju@codeaurora.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>