linux/kernel/rcu/tree_plugin.h, branch v5.17

Merge branches 'doc.2021.11.30c', 'exp.2021.12.07a', 'fastnohz.2021.11.30c', 'fixes.2021.11.30c', 'nocb.2021.12.09a', 'nolibc.2021.11.30c', 'tasks.2021.12.09a', 'torture.2021.12.07a' and 'torturescript.2021.11.30c' into HEAD

2021-12-09T19:38:09Z

doc.2021.11.30c: Documentation updates. exp.2021.12.07a: Expedited-grace-period fixes. fastnohz.2021.11.30c: Remove CONFIG_RCU_FAST_NO_HZ. fixes.2021.11.30c: Miscellaneous fixes. nocb.2021.12.09a: No-CB CPU updates. nolibc.2021.11.30c: Tiny in-kernel library updates. tasks.2021.12.09a: RCU-tasks updates, including update-side scalability. torture.2021.12.07a: Torture-test in-kernel module updates. torturescript.2021.11.30c: Torture-test scripting updates.

rcu: Make idle entry report expedited quiescent states

2021-12-08T00:22:22Z

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 Signed-off-by: Paul E. McKenney

rcu: Remove rcu_data.exp_deferred_qs and convert to rcu_data.cpu no_qs.b.exp

2021-12-08T00:22:21Z

Having two fields for the same purpose with subtle differences on different RCU flavours is confusing, especially when both fields always exist on both RCU flavours. Fortunately, it is now safe for preemptible RCU to rely on the rcu_data structure's ->cpu_no_qs.b.exp field, just like non-preemptible RCU. This commit therefore removes the ad-hoc ->exp_deferred_qs field. Signed-off-by: Frederic Weisbecker Signed-off-by: Paul E. McKenney

rcu: Move rcu_data.cpu_no_qs.b.exp reset to rcu_export_exp_rdp()

2021-12-08T00:22:21Z

On non-preemptible RCU, move clearing of the rcu_data structure's ->cpu_no_qs.b.exp filed to the actual expedited quiescent state report function, matching hw preemptible RCU handles the ->exp_deferred_qs field. This prepares for removing ->exp_deferred_qs in favor of ->cpu_no_qs.b.exp for both preemptible and non-preemptible RCU. Signed-off-by: Frederic Weisbecker Signed-off-by: Paul E. McKenney

rcu: Ignore rdp.cpu_no_qs.b.exp on preemptible RCU's rcu_qs()

2021-12-08T00:20:59Z

Preemptible RCU does not use the rcu_data structure's ->cpu_no_qs.b.exp, instead using a separate ->exp_deferred_qs field to record the need for an expedited quiescent state. In fact ->cpu_no_qs.b.exp should never be set in preemptible RCU because preemptible RCU's expedited grace periods use other mechanisms to record quiescent states. This commit therefore removes the implicit rcu_qs() reference to ->cpu_no_qs.b.exp in favor of a direct reference to ->cpu_no_qs.b.norm. Signed-off-by: Frederic Weisbecker Signed-off-by: Paul E. McKenney

rcu: Avoid running boost kthreads on isolated CPUs

2021-12-01T01:25:20Z

When the boost kthreads are created on systems with nohz_full CPUs, the cpus_allowed_ptr is set to housekeeping_cpumask(HK_FLAG_KTHREAD). However, when the rcu_boost_kthread_setaffinity() is called, the original affinity will be changed and these kthreads can subsequently run on nohz_full CPUs. This commit makes rcu_boost_kthread_setaffinity() restrict these boost kthreads to housekeeping CPUs. Signed-off-by: Zqiang Signed-off-by: Paul E. McKenney

rcu: Improve tree_plugin.h comments and add code cleanups

2021-12-01T01:25:20Z

This commit cleans up some comments and code in kernel/rcu/tree_plugin.h. Signed-off-by: Zhouyi Zhou Signed-off-by: Paul E. McKenney

rcu: in_irq() cleanup

2021-12-01T01:25:20Z

This commit replaces the obsolete and ambiguous macro in_irq() with its shiny new in_hardirq() equivalent. Signed-off-by: Changbin Du Signed-off-by: Paul E. McKenney

rcu: Move rcu_needs_cpu() to tree.c

2021-12-01T01:24:47Z

Now that RCU_FAST_NO_HZ is no more, there is but one implementation of the rcu_needs_cpu() function. This commit therefore moves this function from kernel/rcu/tree_plugin.c to kernel/rcu/tree.c. Signed-off-by: Paul E. McKenney

rcu: Remove the RCU_FAST_NO_HZ Kconfig option

2021-12-01T01:24:47Z

All of the uses of CONFIG_RCU_FAST_NO_HZ=y that I have seen involve systems with RCU callbacks offloaded. In this situation, all that this Kconfig option does is slow down idle entry/exit with an additional allways-taken early exit. If this is the only use case, then this Kconfig option nothing but an attractive nuisance that needs to go away. This commit therefore removes the RCU_FAST_NO_HZ Kconfig option. Signed-off-by: Paul E. McKenney