linux-kernel - Re: [PATCH v3 0/2] Add no-idle tasks check which in dyntick-idle state

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Message-ID: <20220524172855.GP1790663@paulmck-ThinkPad-P17-Gen-1>
Date:   Tue, 24 May 2022 10:28:55 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Zqiang <qiang1.zhang@...el.com>
Cc:     frederic@...nel.org, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 0/2] Add no-idle tasks check which in dyntick-idle
 state

On Tue, May 24, 2022 at 08:34:52AM +0800, Zqiang wrote:
> These commit stop scanning no-idle tasks which in dyntick-idle state and
> remove idle-tasks check from warnings.

This patch might well be correct, but there are supposed to be upcoming
changes in the idle loop that would make it possible for RCU Tasks to
take idle tasks into account:

https://lore.kernel.org/all/20220515203653.4039075-1-jolsa@kernel.org/

There are currently issues in amd_e400_idle() and mwait_idle() preventing
this, and there might well also be similar issues in non-x86 idle loops:

https://lore.kernel.org/all/20220519135439.GX1790663@paulmck-ThinkPad-P17-Gen-1/

So I must hold off on this patch series for the time being.  Nevertheless,
thank you very much for your effort and interest in RCU.

							Thanx, Paul

> v1->v2:
> fix build error when CONFIG_TASKS_RCU=n
> v2->v3:
> remove idle-tasks check from task_is_on_dyntick_idle()
> 
> Zqiang (2):
>   rcu-tasks: Stop RCU Tasks scanning no-idle tasks which record on
>     dyntick-idle entry
>   rcu-tasks: Remove is_idle_task() from warnings in check_holdout_task()
> 
>  kernel/rcu/tasks.h | 16 ++++++++++------
>  1 file changed, 10 insertions(+), 6 deletions(-)
> 
> -- 
> 2.25.1
>