Re: [PATCH 00/11] rcu: Make rcu_core() safe in PREEMPT_RT with NOCB + a few other fixes v2

Paul E. McKenney
2021-10-13T00:32:19Z

On Mon, Oct 11, 2021 at 04:51:29PM +0200, Frederic Weisbecker wrote:
> Hi,
>
> No code change in this v2, only changelogs:
>
> * Add tags from Valentin and Sebastian
>
> * Remove last reference to SEGCBLIST_SOFTIRQ_ONLY (thanks Valentin)
>
> * Rewrite changelog for "rcu/nocb: Check a stable offloaded state to manipulate qlen_last_fqs_check"
> after off-list debates with Paul.
>
> * Remove the scenario with softirq interrupting rcuc on
> "rcu/nocb: Limit number of softirq callbacks only on softirq" as it's
> probably not possible (thanks Valentin).
>
> * Remove the scenario with task spent scheduling out accounted on tlimit
> as it's not possible (thanks Valentin)
> (see "rcu: Apply callbacks processing time limit only on softirq")
>
> * Fixed changelog of
> "rcu/nocb: Don't invoke local rcu core on callback overload from nocb kthread"
> (thanks Sebastian).
>
> git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
> rcu/rt-v2
>
> HEAD: 2c9349986d5f70a555195139665841cd98e9aba4
>
> Thanks,
> Frederic

Nice!

I queued these for further review and testing. I reworked the commit log
of 6/11 to give my idea of the reason, though I freely admit that this
reason is not as compelling as it no doubt seemed when I wrote that code.

Thanx, Paul

> ---
>
> Frederic Weisbecker (10):
> rcu/nocb: Make local rcu_nocb_lock_irqsave() safe against concurrent deoffloading
> rcu/nocb: Prepare state machine for a new step
> rcu/nocb: Invoke rcu_core() at the start of deoffloading
> rcu/nocb: Make rcu_core() callbacks acceleration (de-)offloading safe
> rcu/nocb: Check a stable offloaded state to manipulate qlen_last_fqs_check
> rcu/nocb: Use appropriate rcu_nocb_lock_irqsave()
> rcu/nocb: Limit number of softirq callbacks only on softirq
> rcu: Fix callbacks processing time limit retaining cond_resched()
> rcu: Apply callbacks processing time limit only on softirq
> rcu/nocb: Don't invoke local rcu core on callback overload from nocb kthread
>
> Thomas Gleixner (1):
> rcu/nocb: Make rcu_core() callbacks acceleration preempt-safe
>
>
> include/linux/rcu_segcblist.h | 51 ++++++++++++++++++-------
> kernel/rcu/rcu_segcblist.c | 10 ++---
> kernel/rcu/rcu_segcblist.h | 12 +++---
> kernel/rcu/tree.c | 87 +++++++++++++++++++++++++++++--------------
> kernel/rcu/tree.h | 16 +++++---
> kernel/rcu/tree_nocb.h | 29 ++++++++++++---
> 6 files changed, 141 insertions(+), 64 deletions(-)