My mind was occupied with percpu rcu_preempt_depth for several years since Peter introduced percu preempt_count. But it was stopped by no good way to avoid the scheduler deadlocks. Now we have deferred_qs to avoid the deadlocks, it is time to implement it. During the work, I found two possible? drawbacks (fixed by patch1/2 but patch2 is reverted by patch8 which is a better way). And my not noticing the order of handling special.b.deferred_qs ate many debuging energy (patch7). The percpu rcu_preempt_depth patch is the last patch, patch11. x86 is the only beneficial arch. But other arch can put ->rcu_read_lock_nesting and ->rcu_read_unlock_special to thread_info to avoid the function call after we have patch8/9. CC: Thomas Gleixner <tglx@xxxxxxxxxxxxx> CC: Ingo Molnar <mingo@xxxxxxxxxx> CC: "H. Peter Anvin" <hpa@xxxxxxxxx> CC: x86@xxxxxxxxxx CC: "Paul E. McKenney" <paulmck@xxxxxxxxxx> CC: Josh Triplett <josh@xxxxxxxxxxxxxxxx> CC: Steven Rostedt <rostedt@xxxxxxxxxxx> CC: Lai Jiangshan <jiangshanlai@xxxxxxxxx> CC: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx> CC: Peter Zijlstra <peterz@xxxxxxxxxxxxx> CC: linux-kernel@xxxxxxxxxxxxxxx CC: rcu@xxxxxxxxxxxxxxx Lai Jiangshan (11): rcu: avoid leaking exp_deferred_qs into next GP rcu: fix bug when rcu_exp_handler() in nested interrupt rcu: clean up rcu_preempt_deferred_qs_irqrestore() rcu: cleanup rcu_preempt_deferred_qs() rcu: clean all rcu_read_unlock_special after report qs rcu: clear t->rcu_read_unlock_special in one go rcu: set special.b.deferred_qs before wake_up() rcu: don't use negative ->rcu_read_lock_nesting rcu: wrap usages of rcu_read_lock_nesting rcu: clear the special.b.need_qs in rcu_note_context_switch() x86,rcu: use percpu rcu_preempt_depth arch/x86/Kconfig | 2 + arch/x86/include/asm/rcu_preempt_depth.h | 87 +++++++++++++++ arch/x86/kernel/cpu/common.c | 7 ++ arch/x86/kernel/process_32.c | 2 + arch/x86/kernel/process_64.c | 2 + include/linux/rcupdate.h | 24 +++++ init/init_task.c | 2 +- kernel/fork.c | 2 +- kernel/rcu/Kconfig | 3 + kernel/rcu/tree_exp.h | 58 ++++------ kernel/rcu/tree_plugin.h | 130 +++++++++++++---------- 11 files changed, 220 insertions(+), 99 deletions(-) create mode 100644 arch/x86/include/asm/rcu_preempt_depth.h -- 2.20.1
