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790da24897
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>
Linux kernel
============
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