rcu: Make idle entry report expedited quiescent states

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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>

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This commit is contained in:

Paul E. McKenney 2021-09-29 11:09:34 -07:00

parent 147f04b14a

commit 790da24897

2 changed files with 13 additions and 2 deletions

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2

kernel/rcu/tree.c

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13

kernel/rcu/tree_plugin.h

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