linux-kernel - Re: [PATCH v2 12/14] torture: Replace cpu_up/down with device

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Message-ID: <20191128170025.ii3vqbj4jpcyghut@e107158-lin.cambridge.arm.com>
Date:   Thu, 28 Nov 2019 17:00:26 +0000
From:   Qais Yousef <qais.yousef@....com>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Josh Triplett <josh@...htriplett.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 12/14] torture: Replace cpu_up/down with
 device_online/offline

On 11/28/19 16:56, Qais Yousef wrote:
> On 11/27/19 13:47, Paul E. McKenney wrote:
> > On Mon, Nov 25, 2019 at 11:27:52AM +0000, Qais Yousef wrote:
> > > The core device API performs extra housekeeping bits that are missing
> > > from directly calling cpu_up/down.
> > > 
> > > See commit a6717c01ddc2 ("powerpc/rtas: use device model APIs and
> > > serialization during LPM") for an example description of what might go
> > > wrong.
> > > 
> > > This also prepares to make cpu_up/down a private interface for anything
> > > but the cpu subsystem.
> > > 
> > > Signed-off-by: Qais Yousef <qais.yousef@....com>
> > > CC: Davidlohr Bueso <dave@...olabs.net>
> > > CC: "Paul E. McKenney" <paulmck@...nel.org>
> > > CC: Josh Triplett <josh@...htriplett.org>
> > > CC: linux-kernel@...r.kernel.org
> > 
> > Looks fine from an rcutorture viewpoint, but why not provide an API
> > that pulled lock_device_hotplug() and unlock_device_hotplug() into the
> > online/offline calls?
> 
> I *think* the right way to do what you say is by doing lock_device_hotplug()
> inside device_{online, offline}() - which affects all drivers not just the CPU.
> 
> And even then, I think we need to refcount it so nested calls won't deadlock.

Forget that. I don't think nesting here makes actually any sense.

Thanks

--
Qais Yousef