[PATCH 00/11] rcu: introduce percpu rcu_preempt_depth

Lai Jiangshan
2019-10-31T10:09:25Z

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@linutronix.de>
CC: Ingo Molnar <mingo@redhat.com>
CC: "H. Peter Anvin" <hpa@zytor.com>
CC: x86@kernel.org
CC: "Paul E. McKenney" <paulmck@kernel.org>
CC: Josh Triplett <josh@joshtriplett.org>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Lai Jiangshan <jiangshanlai@gmail.com>
CC: Joel Fernandes <joel@joelfernandes.org>
CC: Peter Zijlstra <peterz@infradead.org>
CC: linux-kernel@vger.kernel.org
CC: rcu@vger.kernel.org

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

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2.20.1