Messages in this thread Patch in this message | | | From | Ankur Arora <> | Subject | [PATCH 15/30] rcu: handle quiescent states for PREEMPT_RCU=n, PREEMPT_COUNT=y | Date | Mon, 12 Feb 2024 21:55:39 -0800 |
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With PREEMPT_RCU=n, cond_resched() provides urgently needed quiescent states for read-side critical sections via rcu_all_qs(). One reason why this was necessary: lacking preempt-count, the tick handler has no way of knowing whether it is executing in a read-side critical section or not.
With PREEMPT_AUTO=y, there can be configurations with (PREEMPT_COUNT=y, PREEMPT_RCU=n). This means that cond_resched() is a stub which does not provide for quiescent states via rcu_all_qs().
So, use the availability of preempt_count() to report quiescent states in rcu_flavor_sched_clock_irq().
Suggested-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Ankur Arora <ankur.a.arora@oracle.com> --- kernel/rcu/tree_plugin.h | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h index 26c79246873a..9b72e9d2b6fe 100644 --- a/kernel/rcu/tree_plugin.h +++ b/kernel/rcu/tree_plugin.h @@ -963,13 +963,16 @@ static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp) */ static void rcu_flavor_sched_clock_irq(int user) { - if (user || rcu_is_cpu_rrupt_from_idle()) { + if (user || rcu_is_cpu_rrupt_from_idle() || + (IS_ENABLED(CONFIG_PREEMPT_COUNT) && + !(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)))) { /* * Get here if this CPU took its interrupt from user - * mode or from the idle loop, and if this is not a - * nested interrupt. In this case, the CPU is in - * a quiescent state, so note it. + * mode, from the idle loop without this being a nested + * interrupt, or while not holding a preempt count. + * In this case, the CPU is in a quiescent state, so note + * it. * * No memory barrier is required here because rcu_qs() * references only CPU-local variables that other CPUs -- 2.31.1
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