linux-kernel - Re: [PATCH] cgroup/cpuset: fix circular locking dependency

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Message-ID: <20180109153752.GI3668920@devbig577.frc2.facebook.com>
Date:   Tue, 9 Jan 2018 07:37:52 -0800
From:   Tejun Heo <tj@...nel.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     Prateek Sood <prsood@...eaurora.org>,
        Peter Zijlstra <peterz@...radead.org>, avagin@...il.com,
        mingo@...nel.org, linux-kernel@...r.kernel.org,
        cgroups@...r.kernel.org, sramana@...eaurora.org
Subject: Re: [PATCH] cgroup/cpuset: fix circular locking dependency

Hello, Paul.

On Tue, Jan 09, 2018 at 07:21:12AM -0800, Paul E. McKenney wrote:
> > The code was previously using both system_power_efficient_wq and
> > system_workqueue (for the expedited path).  I guess the options were
> > either using two workqueues or dropping POWER_EFFICIENT.  I have no
> > idea how big an impact this will make or whether it'd even be
> > noticeable but maybe it'd be worthwhile to mention that in the
> > description?
> 
> Good point!  How about if I change the last paragraph of the commit
> log to read as follows?
> 
> 							Thanx, Paul
> 
> ------------------------------------------------------------------------
> 
> This commit also causes SRCU to use this new RCU-specific
> workqueue_struct.  Note that SRCU's use of workqueues never blocks them
> waiting for readers, so this should be safe from a forward-progress
> viewpoint.  Note that this moves SRCU from system_power_efficient_wq
> to a normal workqueue.  In the unlikely event that this results in 
> measurable degradation, a separate power-efficient workqueue will be
> creates for SRCU.

Sounds good.  Please feel free to add

 Acked-by: Tejun Heo <tj@...nel.org>

Thanks.

-- 
tejun